rootkit.dll: Advanced Defense Evasion Framework from Arsenal-237

A Technical Deep-Dive into Enterprise-Grade Security Product Neutralization and Anti-Forensics Capabilities

Campaign Identifier: Arsenal-237-New-Files-109.230.231.37

Last Updated: January 20, 2026

BLUF (Bottom Line Up Front)

rootkit.dll is a sophisticated defense evasion framework masquerading as a rootkit that weaponizes the Baidu antivirus driver (BdApiUtil64.sys) via BYOVD techniques to systematically disable 20+ security products and forensic tools. This modular component integrates file hiding, API hooking, and PowerShell-based anti-forensics to enable undetected ransomware operations, making it a critical enabler in the Arsenal-237 attack toolkit.

Table of Contents

  1. Quick Reference
  2. Executive Summary
  3. Overview and Arsenal-237 Context
  4. Critical Clarification: NOT a Traditional Rootkit
  5. Primary Capabilities
  6. Technical Architecture
  7. Embedded Driver Analysis: BdApiUtil64.sys Weaponization
  8. Target Security Products: Comprehensive List
  9. Attack Chain Integration
  10. Evolution from killer.dll
  11. MITRE ATT&CK Mapping
  12. Detection Opportunities
  13. Threat Assessment
  14. Remediation Guidance
  15. Response Priorities
  16. Key Takeaways
  17. Indicators of Compromise

Quick Reference

Detections & IOCs:

Related Reports:

Executive Summary

rootkit.dll represents a significant evolution in defense evasion frameworks within the Arsenal-237 toolkit. While the filename suggests kernel-mode rootkit functionality, this component is better understood as a comprehensive defense neutralization framework that combines Bring-Your-Own-Vulnerable-Driver (BYOVD) exploitation, user-mode stealth capabilities, and anti-forensics operations into a single modular payload.

The component’s primary contribution to the Arsenal-237 attack chain is systematic elimination of security products that would otherwise detect subsequent attack stages. By embedding the Baidu antivirus driver (BdApiUtil64.sys version 5.0.3.84333) and implementing file hiding and API hooking routines, rootkit.dll creates a hostile environment where defenders cannot monitor, analyze, or respond to follow-on attacks. This positions rootkit.dll as a critical enabler for undetected ransomware deployment against hardened environments protected by enterprise security solutions.

The framework demonstrates professional-grade development with clear modular architecture, sophisticated function dispatching, and comprehensive targeting of both mainstream security products and forensic/analysis tools. Its integration into Arsenal-237 reflects a mature threat actor operation with deep understanding of defensive environments and the ability to weaponize legitimate but vulnerable drivers against their operators.

Key Risk Factors:

Risk Factor Score Business Impact
Overall Threat Severity 9.2/10 CRITICAL - Enables undetected ransomware operations and data exfiltration
Security Product Neutralization 9.5/10 20+ products systematically disabled via kernel-level access
Persistence Capability 9.0/10 Kernel driver deployment survives user-mode cleanup attempts
Anti-Forensics Effectiveness 8.5/10 File hiding and API hooking prevent incident investigation
Analysis Tool Evasion 8.0/10 Targets Process Explorer, debuggers, network analysis, memory forensics
Detection Difficulty 7.8/10 BYOVD driver signature is legitimate; behavioral detection required

For Executive Leadership:

  • Systems infected with rootkit.dll have experienced compromise of core security infrastructure
  • Kernel-level access enables attackers to bypass security controls and investigate environments undetected
  • Immediate system isolation and forensic preservation are mandatory
  • Complete system rebuild is required for reliable remediation
  • Implement administrative controls to block vulnerable driver exploitation on remaining systems

For Technical Teams:

  • Deploy detection signatures urgently to identify rootkit.dll samples and embedded BdApiUtil64.sys driver
  • Conduct threat hunting for Arsenal-237 toolkit components (lpe.exe, killer.dll, nethost.dll, enc_*.exe)
  • Review firewall and endpoint logs for the identified timeframe when rootkit.dll was active
  • Enable Vulnerable Driver Blocklist (Windows 11 HVCI) to prevent future BYOVD exploitation
  • Implement kernel-mode protection mechanisms to detect driver loading from non-standard locations

Overview and Arsenal-237 Context

rootkit.dll is the fifth of eleven deep-dive samples analyzed as part of Arsenal-237 threat actor infrastructure. This component was discovered on an open directory at 109.230.231.37 alongside a comprehensive attack toolkit containing privilege escalation, security product termination, driver exploitation, command and control, and ransomware payloads.

Arsenal-237 Toolkit Composition:

Component Function Status
lpe.exe Privilege escalation wrapper; elevates killer.dll to SYSTEM Analyzed
killer.dll Basic BYOVD-based process termination via BdApiUtil64.sys Analyzed
killer_crowdstrike.dll Specialized CrowdStrike termination with expanded targeting Analyzed
BdApiUtil64.sys Baidu antivirus driver v5.0.3.84333; kernel-mode driver exploited via BYOVD Analyzed
rootkit.dll Comprehensive defense evasion framework with stealth and anti-forensics THIS REPORT
nethost.dll C2 communication handler for command execution and data exfiltration Pending
enc_*.exe Ransomware payloads with encryption and file modification Pending

The toolkit demonstrates a well-organized modular attack framework with clear functional separation: privilege escalation enables defense evasion, which enables C2 establishment, which enables ransomware deployment. rootkit.dll occupies a critical position in this progression by creating the hostile defensive environment necessary for subsequent attack stages.

Critical Clarification: NOT a Traditional Rootkit

The filename “rootkit.dll” is misleading. This component is NOT a traditional kernel-mode rootkit designed to hide running processes, network connections, or file system artifacts from kernel inspection tools. Instead, rootkit.dll is an Advanced Defense Evasion Framework that combines multiple attack vectors into a single modular payload.

Traditional Rootkit Expectations vs. rootkit.dll Reality:

Characteristic Traditional Rootkit rootkit.dll
Primary Function Process/file/connection hiding from kernel Security product neutralization + stealth support
Deployment Method Kernel-mode driver installation BYOVD exploitation of legitimate driver
Evasion Target Kernel-aware forensics tools User-mode security products + analysis tools
Stealth Mechanism Hook kernel data structures (EPROCESS, FILE_OBJECT) API hooking + file system manipulation
Typical Capability Hide single malware process from view Disable 20+ security products systematically

rootkit.dll’s actual purpose is defense neutralization and anti-forensics rather than stealth process hiding. The naming reflects either a marketing choice or a code organization pattern, but the functionality is clearly oriented toward eliminating defensive capabilities rather than hiding individual artifacts.

Primary Capabilities

rootkit.dll implements six major capability categories that work together to create a comprehensive defense evasion framework:

1. BYOVD (Bring Your Own Vulnerable Driver) Exploitation

rootkit.dll weaponizes the Baidu antivirus driver (BdApiUtil64.sys version 5.0.3.84333) through BYOVD exploitation. This driver is the same legitimate but vulnerable component embedded in killer.dll and analyzed separately as a standalone toolkit element.

Technical Details:

  • Driver: BdApiUtil64.sys (Baidu Antivirus v5.0.3.84333)
  • Signature: Legitimately signed by Baidu (certificate expired 2015, but Windows still accepts)
  • IOCTL Code: 0x800024B4 (arbitrary kernel memory write/read capability)
  • Device Objects: \Device\BdApiUtil
  • Symbolic Link: \DosDevices\BdApiUtil
  • Service Name: Bprotect
  • PDB Path: D:\jenkins\workspace\bav_5.0_workspace\BavOutput\Pdb\Release\BdApiUtil64.pdb

Exploitation Flow:

  1. rootkit.dll extracts embedded BdApiUtil64.sys driver from resource section
  2. Writes driver to temporary location (typically System32 or Drivers directory)
  3. Creates Bprotect service pointing to driver
  4. Loads service to elevate to Ring-0 (kernel-mode) privileges
  5. Uses IOCTL 0x800024B4 to enable arbitrary kernel operations

Ring-0 Privileges Enable:

  • Process termination with SYSTEM privileges (bypasses user-mode restrictions)
  • Direct memory manipulation for API hooking
  • File system access bypassing user-mode filters
  • Registry manipulation without security product intervention

2. Comprehensive Process Termination (20+ Security Products)

rootkit.dll implements systematic termination of 20+ security products across seven major categories. This capability uses the embedded BdApiUtil64.sys driver to achieve SYSTEM-level process termination, ensuring that even processes running at highest privileges cannot resist.

Microsoft Defender Products (10 processes):

  • MsMpEng.exe - Main antivirus engine (AV scanning)
  • MpDefenderCoreService.exe - Core protection service
  • NisSrv.exe - Network Inspection Service (network-based detection)
  • smartscreen.exe - SmartScreen filter (phishing/malware URL blocking)
  • MsSense.exe - Defender ATP/EDR main agent
  • SenseCnProxy.exe - Cloud protection proxy
  • SenseIR.exe - Incident response component
  • SecurityHealthService.exe - Health monitoring service
  • SecurityHealthSystray.exe - System tray UI component
  • MpCmdRun.exe - Command-line utility (configuration/deployment)

CrowdStrike Falcon Products (6 processes):

  • CSFalconService.exe - Main EDR service
  • csagent.exe - Agent process (monitoring/detection)
  • CSFalconContainer.exe - Container isolation service
  • SentinelAgent.exe - Sentinel integration component
  • SentinelServiceHost.exe - Service hosting
  • SentinelStaticEngine.exe - Static analysis engine

ESET Products (4 processes):

  • ekrn.exe - ESET kernel process (AV engine)
  • egui.exe - ESET graphical interface
  • eamonm.exe - ESET file monitor
  • eset.exe - ESET service

Kaspersky Products (3 processes):

  • avp.exe - Kaspersky AV process
  • kavfs.exe - Kaspersky file system monitor
  • kavfsslp.exe - Kaspersky file system sleeper

Bitdefender Products (2 processes):

  • bdagent.exe - Bitdefender agent
  • ebdagent.exe - Bitdefender extended agent

Malwarebytes Products (4 processes):

  • MBAMService.exe - Main service
  • mbamtray.exe - System tray component
  • MBAMWsc.exe - Windows Security Center integration
  • MBAMSwissArmy.exe - Multi-function utility

Symantec Products (3 processes):

  • SepMasterService.exe - Symantec Endpoint Protection master service
  • ccSvcHst.exe - Symantec core service host
  • Rtvscan.exe - Real-time scan process

McAfee Products (4 processes):

  • mfefire.exe - McAfee firewall
  • mfemms.exe - Memory management service
  • mmcshield.exe - On-access scanner
  • coreServiceShell.exe - Core service shell

Other Major Vendors (8 processes):

  • cb.exe - Carbon Black agent
  • CbDefense.exe - CB Defense
  • RepMgr.exe - CB Repository Manager
  • SophosHealth.exe - Sophos Health
  • SophosFileScanner.exe - Sophos file scanning
  • SophosUI.exe - Sophos user interface
  • CylanceSvc.exe - Cylance service
  • CortexXDR.exe - Palo Alto Cortex XDR

Termination Mechanism:

The process termination flow uses kernel-mode capabilities provided by BdApiUtil64.sys:

  1. Enumerate running processes with SYSTEM privileges
  2. Match process names against hard-coded termination list
  3. Use IOCTL 0x800024B4 to terminate process from kernel
  4. Bypass user-mode restrictions and process protection

Behavioral Characteristics:

  • Multiple process terminations within 60 seconds of execution
  • Processes terminate despite having active security monitoring
  • No user-mode error codes or process termination callbacks triggered
  • Terminations appear to originate from system-level operations (difficult to attribute to rootkit.dll from user-space)

3. File System Stealth via Unicode Obfuscation

rootkit.dll implements sophisticated file hiding through Unicode-based obfuscation within the file system layer. This capability (implemented in sub_180003c4b) uses multi-byte character processing to hide malicious files from directory enumeration and file system browsing.

Technical Implementation:

  • Function: sub_180003c4b (File System Stealth)
  • Technique: Unicode-based file hiding
  • Method: Multi-byte character processing for obfuscation
  • Operations:
    • Buffer shifting to reposition file names
    • Byte replacement (0xff substitution)
    • Character-level manipulation of file paths
    • Path obfuscation to prevent directory traversal

Practical Effect:

  • Ransomware files (encrypted payloads, ransom notes) hidden from directory browsing
  • Malicious DLLs and executables concealed from file managers
  • Directory listings appear incomplete to security tools
  • Windows Explorer and command-line dir commands may skip hidden entries

API Hooking Integration: This stealth capability works in conjunction with API hooking (described below) to maintain consistent hiding across different file access APIs:

  • FindFirstFileW/FindNextFileW (directory enumeration)
  • CreateFileW/OpenFileW (file opening)
  • ReadDirectoryW (directory reading)
  • GetFileAttributesW (attribute queries)

4. API Hooking for Call Interception

rootkit.dll implements API hooking (sub_180003447) to intercept and redirect file system and security-related API calls. This mechanism enables consistent hiding of malicious files across different API entry points.

Technical Details:

  • Function: sub_180003447 (API Hooking Implementation)
  • Encoding: UTF-8 processing (1-4 byte character encoding)
  • Target APIs: File system and security monitoring APIs
  • Mechanism: Inline API hooking with redirection

Hooked API Categories:

  1. File System Discovery APIs:
    • Hooks that prevent directory enumeration APIs from returning hidden files
    • Redirection to alternate file paths or filtered results
  2. Process Monitoring APIs:
    • Hooks that conceal process creation
    • Redirection of process enumeration queries
  3. Registry Monitoring APIs:
    • Hooks to hide malicious registry entries
    • Redirection of registry enumeration
  4. Security Product APIs:
    • Hooks to disable security monitoring
    • Redirection of threat alerts

Behavioral Signature:

  • Unicode string processing operations (0x180003447 region)
  • UTF-8 encoding manipulation
  • Function pointer tables for hooked APIs
  • Indirect call patterns indicating redirection

5. PowerShell Integration and Script Execution

rootkit.dll includes PowerShell integration capabilities enabling script-based attack execution while benefiting from rootkit.dll’s defense evasion protections.

Technical Details:

  • Target Process: powershell.exe
  • Execution Method: Script-based commands
  • Privilege Level: SYSTEM (through rootkit.dll elevation)
  • Evasion Benefit: PowerShell execution occurs in environment with neutralized security products

Attack Scenarios:

  • Credential harvesting using PowerShell modules
  • Registry manipulation for persistence
  • WMI-based lateral movement commands
  • Script-based ransomware triggering
  • Command obfuscation using PowerShell encoding

Integration with Arsenal-237: The PowerShell integration enables flexible attack execution after rootkit.dll has eliminated security products, allowing threat actors to execute complex multi-stage commands without modification between environments.

6. Anti-Forensics and Analysis Tool Targeting

rootkit.dll systematically targets forensic and analysis tools to prevent malware investigation and incident response. This comprehensive anti-forensics capability ensures that even post-incident analysis becomes significantly more difficult.

Targeted Analysis Tools:

Category Tools Impact
Process Exploration Process Explorer, Process Hacker, SystemInformer Cannot enumerate running processes; hidden rootkit operations undetectable
Debugging x64dbg, x32dbg, Ollydbg, Windbg, IDA Malware reverse engineering blocked; payload analysis impossible
Network Analysis Wireshark, Tshark, TCPView, Netmon, NetworkMiner, Fiddler, Charles, Burp Suite C2 traffic capture prevented; command protocol unrecoverable
Memory Forensics Volatility, DumpIt, RamCapture Memory dumps become unreliable; malware state unrecoverable
Remediation Tools Sysinternals (autoruns, handle, listdlls, strings), Malwarebytes, RogueKiller, FRST Cleanup verification impossible; residual malware undetectable

Forensic Evasion Strategy: By targeting both active analysis tools and post-incident forensic utilities, rootkit.dll creates conditions where:

  • Real-time detection becomes impossible (security products terminated)
  • Post-incident investigation becomes severely hampered (forensic tools targeted)
  • Incident response procedures become unreliable (analysis tools nonfunctional)
  • Recovery verification becomes uncertain (cleanup verification tools disabled)

Technical Architecture

rootkit.dll demonstrates sophisticated modular architecture implemented in Rust with clear functional separation and advanced execution patterns.

Rust Runtime and Compilation

rootkit.dll is compiled with the Rust compiler (rustc) into a PE64 DLL binary:

  • File: rootkit.dll
  • Size: 413,696 bytes (404 KB)
  • Architecture: x64 (64-bit)
  • Format: Windows PE DLL
  • Compiler: Rust (rustc)
  • Signature: Unsigned

The Rust runtime provides:

  • Standard error handling mechanisms
  • Memory management and cleanup
  • Thread creation and coordination
  • Configuration loading from embedded data structures

Entry Point and Initialization

Primary Entry Points:

Function Offset Purpose
_start 0x1800011f0 Initial entry point dispatcher
DllMain 0x1800042ff Core DLL initialization
sub_180001000 N/A Runtime init/cleanup

Initialization Flow:

DllMain (entry)
  |
Load configuration from data_18003af70
  |
Initialize Rust runtime
  |
Dispatch to thread creation (sub_180035420)
  |
Transition to thread entry wrapper (sub_1800355b0)
  |
Indirect dispatch to core payload

Thread-Based Execution Model

rootkit.dll uses a multi-threaded execution model to isolate defense evasion operations from the calling process:

Thread Creation: sub_180035420

  • Creates new thread for defense evasion payload
  • Thread operates asynchronously from main process
  • Enables rootkit.dll to complete execution before security products terminate
  • Allows payload to continue even if calling process exits

Thread Entry Wrapper: sub_1800355b0

  • Receives execution context
  • Manages function dispatch via indirect call
  • Provides abstraction layer between thread creation and actual payload
  • Function pointer at offset +0x18 in context structure

Execution Isolation:

  • Defense evasion operations run in separate thread
  • Main thread returns control to caller (process injection appears normal)
  • Caller process unaware of ongoing operations
  • Provides stealth through process behavior appearance

Core Defense Evasion Orchestrator

Function: sub_180002f7b (Core Payload)

This function represents the central orchestrator coordinating all defense evasion operations:

Internal Structure:

sub_180002f7b (Main Orchestrator)
  +- sub_180003209 (Setup Phase)
  |   +- Extract embedded BdApiUtil64.sys driver
  |   +- Load driver to create Ring-0 access
  |   +- Initialize IOCTL communication
  |
  +- sub_1800032ba (Function Dispatcher Loop)
  |   +- Function Array with 10+ defense evasion functions
  |   +- Parameter structures for each function
  |   +- Cleanup handlers for reference counting
  |   +- Sequential execution of evasion operations
  |
  +- sub_180003379 (Cleanup Phase)
      +- Finalize driver communication
      +- Release resources
      +- Reset system state

Sophisticated Function Dispatcher

Function: sub_1800032ba (Dispatcher Loop)

This function implements a sophisticated dispatcher executing multiple defense evasion functions sequentially:

Dispatcher Characteristics:

  • Executes array of function pointers with configurable ordering
  • Maintains reference counting for resource management
  • Provides cleanup handlers for each function
  • Supports parameter passing through structure arrays
  • Implements error handling and partial failure modes

Execution Model:

FOR each defense evasion function in array
  +- Load function parameters from structure
  +- Execute function with Ring-0 privileges
  +- Capture execution result
  +- Invoke cleanup handler if needed
  +- Continue to next function

Function Categories:

  1. Driver Operations - BdApiUtil64.sys deployment and communication
  2. Process Termination - Enumerate and terminate security products
  3. File System Hiding - Unicode-based file path obfuscation
  4. API Hooking - Intercept and redirect file system APIs
  5. PowerShell Integration - Enable script execution
  6. Anti-Forensics - Target analysis tool processes

Cleanup Phase

Function: sub_180003379 (Cleanup)

After all defense evasion operations complete, the cleanup phase:

  • Finalizes driver communication
  • Releases kernel resources
  • Resets thread state
  • Removes execution artifacts

This structure ensures that rootkit.dll’s operational presence is minimized after defenses are compromised, reducing the likelihood of behavioral detection.

Embedded Driver Analysis: BdApiUtil64.sys Weaponization

rootkit.dll embeds the same Baidu antivirus driver (BdApiUtil64.sys) used in killer.dll and deployed separately in Arsenal-227 infrastructure. This represents systematic BYOVD exploitation of a single vulnerable driver across multiple toolkit components.

Driver Metadata

Property Value
Driver Name BdApiUtil64.sys
Vendor Baidu (Baidu Antivirus)
Version 5.0.3.84333
Signature Baidu (Expired 2015, but still accepted by Windows)
Architecture x64
PDB Path D:\jenkins\workspace\bav_5.0_workspace\BavOutput\Pdb\Release\BdApiUtil64.pdb

Vulnerability and Exploitation

The Baidu driver contains an unprotected IOCTL interface allowing unprivileged user-mode code to perform kernel-level operations:

IOCTL Code: 0x800024B4 Capability: Arbitrary kernel memory write/read Attack: Process termination with kernel privileges (bypassing user-mode restrictions)

Deployment and Loading

rootkit.dll extracts and deploys BdApiUtil64.sys through standard Windows driver mechanisms:

  1. Extraction: Embedded driver extracted from rootkit.dll resource section
  2. Placement: Typically written to System32\Drivers or temporary location
  3. Service Creation: Creates “Bprotect” service registry entries
  4. Service Start: Loads service, triggering Windows driver signature validation
  5. Kernel Loading: Windows loads legitimately-signed driver despite BYOVD intention

Service Registry Structure:

HKLM\SYSTEM\CurrentControlSet\Services\Bprotect
  +- Type: REG_DWORD = 1 (kernel driver)
  +- Start: REG_DWORD = 2 (load at boot)
  +- ImagePath: REG_SZ = System32\Drivers\BdApiUtil64.sys
  +- DisplayName: Baidu Antivirus Driver
  +- [Additional service configuration]

Ring-0 Capability Leverage

Once loaded, BdApiUtil64.sys operates at Ring-0 (kernel privilege level), enabling:

Process Termination at SYSTEM Level:

  • Enumerate all running processes from kernel
  • Terminate SYSTEM-level security processes (cannot resist from user-mode)
  • Bypass process protection mechanisms
  • Disable security product monitoring

Memory Manipulation:

  • Direct kernel memory read/write via IOCTL 0x800024B4
  • Enable API hooking by modifying kernel data structures
  • Modify process memory without triggering user-mode security callbacks

File System Access:

  • Bypass user-mode file system filters
  • Access files hidden by security products
  • Modify file system directly

Comparison to Standalone BdApiUtil64.sys Analysis

rootkit.dll’s use of BdApiUtil64.sys is nearly identical to the standalone toolkit component, with one critical difference:

Standalone Deployment: BdApiUtil64.sys deployed alone for basic process termination (simple BYOVD exploitation)

rootkit.dll Integration: BdApiUtil64.sys embedded within comprehensive evasion framework, providing Ring-0 foundation for multiple attack vectors (process termination + file hiding + API hooking + anti-forensics)

This represents escalation from standalone driver exploitation to integrated multi-vector attack framework.

Target Security Products: Comprehensive List

rootkit.dll targets 20+ security products organized across multiple vendor categories. This comprehensive targeting reflects extensive research into defender environments and professional-grade threat actor operations.

Targeting Strategy

The product list reveals strategic targeting decisions:

  1. Market Share Coverage: Targets products with highest enterprise deployment
  2. EDR Priority: Emphasizes EDR products (Defender ATP, CrowdStrike) due to detection risk
  3. Legacy Support: Includes older products (Kaspersky, Symantec) for wide environment coverage
  4. Tool Targeting: Targets both security products and forensic analysis tools
  5. Complete Elimination: Not selective - attempts to disable ALL identified products simultaneously

Product Categories and Impact Assessment

Microsoft Defender (10 processes) - CRITICAL PRIORITY:

The targeting of Defender’s 10 processes represents comprehensive elimination:

  • MsMpEng.exe (AV Engine) - Primary antivirus scanning component
  • NisSrv.exe (Network Inspection) - Network-based threat detection
  • MsSense.exe (Defender ATP) - Enterprise EDR agent
  • smartscreen.exe (Phishing Protection) - URL and file reputation checking

Impact: Organizations relying primarily on Windows Defender lose all antivirus, EDR, and network-based detection.

CrowdStrike Falcon (6 processes) - ENTERPRISE IMPACT:

CrowdStrike receives specialized focus with 6 targeted processes:

  • CSFalconService.exe (Main Service)
  • csagent.exe (Agent Process)
  • CSFalconContainer.exe (Container Isolation)
  • SentinelAgent.exe (Integration)
  • SentinelServiceHost.exe (Service Host)
  • SentinelStaticEngine.exe (Analysis)

Impact: Comprehensive elimination of CrowdStrike’s detection, isolation, and response capabilities.

ESET, Kaspersky, Bitdefender (9 processes combined):

Traditional antivirus vendors receive targeted elimination:

  • ESET: 4 processes (ekrn, egui, eamonm, eset)
  • Kaspersky: 3 processes (avp, kavfs, kavfsslp)
  • Bitdefender: 2 processes (bdagent, ebdagent)

Impact: Traditional signature-based and behavioral detection eliminated.

Extended Security Portfolio (15+ processes):

Malwarebytes, Symantec, McAfee, CB Defense, Sophos, Cylance, and Cortex XDR receive targeted elimination, representing comprehensive coverage of alternative security solutions organizations might deploy.

Detection Difficulty Due to Comprehensive Targeting

The breadth of targeting creates a strategic problem for defenders:

  • Selective Response: An organization cannot rely on any single security product as detection source
  • Backup Elimination: Primary detection backup eliminated by specialist DLL (killer_crowdstrike.dll)
  • Tool Targeting: Even post-incident analysis tools are disabled
  • Complete Blindness: Organizations experience complete loss of security visibility

Attack Chain Integration

rootkit.dll occupies a specific position within the Arsenal-237 attack progression:

Arsenal-237 Attack Sequence

Stage 1: Initial Access (External)
  +- Compromised website or phishing campaign delivers lpe.exe

Stage 2: Privilege Escalation (lpe.exe)
  +- lpe.exe wraps and executes killer.dll
  +- Privilege escalation elevates to SYSTEM

Stage 3: Defense Evasion - Phase 1 (rootkit.dll)  <- THIS COMPONENT
  +- Extract and load BdApiUtil64.sys driver
  +- Terminate initial security products (broad coverage)
  +- Deploy file hiding and API hooking
  +- Target forensic and analysis tools
  +- Establish PowerShell integration

Stage 4: Defense Evasion - Phase 2 (killer_crowdstrike.dll or nethost.dll)
  +- Option A: killer_crowdstrike.dll for specialized EDR targeting
  +- Option B: nethost.dll to establish C2 communication channel

Stage 5: C2 Establishment (nethost.dll)
  +- Connect to Arsenal-237 command infrastructure
  +- Receive attack directives
  +- Establish reverse shell or RDP access

Stage 6: Ransomware Deployment (enc_*.exe)
  +- Execute ransomware payload under rootkit.dll protection
  +- Encrypt files with disabled security monitoring
  +- Extend encryption to network resources through C2 commands
  +- Demand ransom payment

Stage 7: Extortion (Demand/Communication)
  +- Deliver ransom notes (hidden via rootkit.dll file hiding)
  +- Communicate payment demands through C2

rootkit.dll’s Critical Role

rootkit.dll serves as the bridge between privilege escalation and ransomware deployment. Without this component:

  • Privilege Escalation Insufficient: SYSTEM privileges alone insufficient for defense neutralization (processes can be re-launched)
  • Ransomware Vulnerable: Ransomware execution would immediately trigger security product detection
  • Investigation Enabled: Incident response tools would provide detection and recovery options

With rootkit.dll:

  • Comprehensive Defense: Ring-0 privileges enable systematic elimination + file hiding + anti-forensics
  • Undetected Encryption: Ransomware executes in environment with neutralized monitoring
  • Investigation Prevention: Forensic tools targeted to prevent post-incident analysis
  • Recovery Denial: File hiding prevents victim verification of protection restoration

Redundancy and Escalation

The toolkit includes multiple defense evasion components (killer.dll, killer_crowdstrike.dll, rootkit.dll) reflecting defensive redundancy strategy:

  • killer.dll: General-purpose BYOVD-based termination
  • killer_crowdstrike.dll: Specialized CrowdStrike targeting
  • rootkit.dll: Comprehensive framework with file hiding + anti-forensics

This redundancy ensures that even if one component fails or is detected, alternatives remain available.

Evolution from killer.dll

rootkit.dll represents a significant evolution from killer.dll, the basic BYOVD-based process termination component. Understanding this evolution illuminates Arsenal-237 threat actor maturation and refinement of attack techniques.

Functional Comparison

Aspect killer.dll rootkit.dll
Primary Function Process termination only Comprehensive defense evasion framework
Embedded Driver BdApiUtil64.sys Same BdApiUtil64.sys
IOCTL Usage 0x800024B4 (termination) 0x800024B4 + additional capabilities
Target Processes 20+ security products Same 20+ products
File Hiding Not implemented Unicode-based obfuscation
API Hooking Not implemented UTF-8 processing for call interception
Anti-Forensics Targets security products Targets products + forensic tools + debuggers
PowerShell Integration Not implemented Script execution support
Sophistication Single-vector attack Multi-vector defense framework

Strategic Implications of Evolution

killer.dll Limitations:

  • Process termination alone does not prevent re-launching (Windows auto-restarts some services)
  • Does not hide malware files or network activity
  • Does not prevent post-incident forensic investigation
  • Provides only temporary defense suppression

rootkit.dll Advantages:

  • File hiding + API hooking create persistent stealth layer
  • Ring-0 privileges prevent security product restart
  • Forensic tool targeting prevents investigation
  • PowerShell integration enables flexible attack execution
  • Multi-vector framework creates conditions for undetected ransomware

This evolution reflects threat actor learning and optimization over time. Initial toolkit included basic BYOVD exploitation, but Arsenal-237 developers recognized limitations and created comprehensive defense evasion framework (rootkit.dll) addressing those gaps.

Code Architecture Evolution

killer.dll Architecture: Simple termination loop

  • Enumerate processes
  • Match against termination list
  • Use IOCTL to terminate
  • Exit

rootkit.dll Architecture: Sophisticated multi-function dispatcher

  • Setup phase (driver deployment)
  • Dispatcher loop executing 6+ defense evasion functions
  • Parameter structures enabling flexible configuration
  • Cleanup phase (resource release)
  • Thread-based isolation

This architectural progression reflects professional software engineering practices applied to malware development.

MITRE ATT&CK Mapping

rootkit.dll’s capabilities map to multiple MITRE ATT&CK techniques across Defense Evasion, Privilege Escalation, Persistence, Execution, and Anti-Analysis categories:

Tactic Technique ID Technique Name rootkit.dll Implementation Confidence
Defense Evasion T1562.001 Impair Defenses: Disable or Modify Tools Systematic termination of 20+ security products; CRITICAL capability CONFIRMED
Defense Evasion T1564.001 Hide Artifacts: Hidden Files and Directories Unicode-based file hiding via sub_180003c4b CONFIRMED
Defense Evasion T1027.010 Obfuscated Files: Command Obfuscation PowerShell integration with command obfuscation via UTF-8 processing CONFIRMED
Defense Evasion T1112 Modify Registry Manipulate registry for persistence and configuration (Bprotect service) HIGHLY LIKELY (95%)
Defense Evasion T1055.001 Process Injection: Dynamic Execution DLL injection via rundll32.exe execution; thread-based payload delivery CONFIRMED
Privilege Escalation T1068 Exploitation for Privilege Escalation Exploits Baidu driver (BdApiUtil64.sys) IOCTL 0x800024B4 for Ring-0 access CONFIRMED
Persistence T1543.003 Create or Modify System Process: Windows Service Creates Bprotect service for BdApiUtil64.sys driver loading CONFIRMED
Execution T1059.001 Command and Scripting Interpreter: PowerShell PowerShell integration enabling script-based command execution at SYSTEM privileges CONFIRMED
Execution T1106 Native API Execution Uses kernel APIs via BdApiUtil64.sys IOCTL interface for Ring-0 operations CONFIRMED
Impact T1529 System Shutdown/Reboot Targets system management and recovery tools that could restore defenses LIKELY (70%)

Technique Justification

T1562.001 - Impair Defenses (CRITICAL):

  • CONFIRMED through process termination list (20+ security products)
  • CONFIRMED through BYOVD exploitation of BdApiUtil64.sys IOCTL
  • Code reference: sub_180002f7b dispatcher loop

T1564.001 - Hide Artifacts:

  • CONFIRMED through Unicode file hiding (sub_180003c4b)
  • CONFIRMED through API hooking (sub_180003447)
  • Practical effect: Ransomware files hidden from directory enumeration

T1027.010 - Command Obfuscation:

  • CONFIRMED through PowerShell integration
  • CONFIRMED through UTF-8 encoding manipulation in API hooking
  • Behavioral indicator: Obfuscated command execution

T1068 - Exploitation for Privilege Escalation:

  • CONFIRMED through BdApiUtil64.sys BYOVD exploitation
  • CONFIRMED through IOCTL 0x800024B4 leveraging
  • Ring-0 privilege access enables all other capabilities

T1543.003 - Windows Service Creation:

  • CONFIRMED through Bprotect service creation
  • Service loads BdApiUtil64.sys driver with kernel privileges
  • Registry manipulation creates persistence mechanism

T1059.001 - PowerShell Execution:

  • CONFIRMED through PowerShell integration targeting
  • SYSTEM-level execution enabled by rootkit.dll privileges
  • Script-based attack execution supported

Detection Opportunities

rootkit.dll presents multiple detection vectors across file-based, behavioral, runtime, and forensic artifact categories. Detection effectiveness varies based on available security infrastructure.

File-Based Detection

Hash-Based Signatures (Highest Confidence):

Hash Type Value
SHA256 e71240f26af1052172b5864cdddb78fcb990d7a96d53b7d22d19f5dfccdf9012
SHA1 483feeb4e391ae64a7d54637ea71d43a17d83c71
MD5 674795d4d4ec09372904704633ea0d86

YARA Detection (File Properties):

rule Arsenal237_rootkit_dll_FileProperties {
    strings:
        $pe_sig_1 = "MZ" at 0
        $pe_sig_2 = "PE\x00\x00" at 0x3C
        $size = { ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? }
        $rust_artifact = "rustc"
    condition:
        uint16(0) == 0x5A4D and
        uint32(uint32(0x3C)) == 0x4550 and
        filesize == 413696 and
        any of them
}

Detection Strength: CONFIRMED hash match = certain identification (Detection Confidence: DEFINITE)

Behavioral Detection

Execution Pattern Detection:

  1. rundll32.exe Execution with rootkit.dll: 
    rundll32.exe rootkit.dll DllEntryPoint
    • Presence of rootkit.dll in rundll32 command line triggers alert
    • Detection Confidence: DEFINITE (process execution is observable)
  2. Mass Security Product Termination: ``` Process Termination Event Stream:
    • MsMpEng.exe terminated
    • NisSrv.exe terminated
    • CSFalconService.exe terminated
    • [20+ processes within 60 seconds] ```
    • Multiple security product terminations in rapid sequence
    • Detection Confidence: DEFINITE (observable behavioral pattern)
    • Typical Timeline: 20+ terminations within 60 seconds of rootkit.dll execution
  3. BdApiUtil64.sys Driver Deployment:
    • Extraction of driver from resource section (observable only with hooking)
    • Writing to System32\Drivers or temporary location (observable via file monitoring)
    • Service creation for Bprotect (observable via registry monitoring)
    • Detection Confidence: DEFINITE (driver loading triggers kernel events)
  4. API Hooking Indicators:
    • Unicode string manipulation operations (function addresses: 0x180003447)
    • UTF-8 processing loops targeting Windows APIs
    • Function pointer table creation for API redirection
    • Detection Confidence: HIGHLY LIKELY (requires memory analysis tools)

Behavioral Detection Mechanisms:

Behavior Detection Method Effectiveness
Mass process termination Sysmon Event ID 5 or EDR process termination events HIGH - Rapid termination sequence observable
Driver loading Sysmon Event ID 6 (Driver Loaded) DEFINITE - Kernel event generated
Service creation Registry monitoring or Event ID 4697 DEFINITE - Service creation logged
File system operations File monitoring on System32\Drivers HIGH - Driver file observable
API hooking Kernel-mode monitoring or memory inspection MEDIUM - Requires advanced tooling

Runtime Detection - Driver and Service Indicators

Forensic Artifacts to Monitor:

  1. Service Registry Keys: 
    HKLM\SYSTEM\CurrentControlSet\Services\Bprotect
HKLM\SYSTEM\CurrentControlSet\Services\Bprotect\Parameters
    • Presence indicates driver loading attempt
    • Service name “Bprotect” specific to Arsenal-227 toolkit
    • Detection Confidence: DEFINITE (registry persistence)
  2. Driver Loading:
    • Device Object: \Device\BdApiUtil
    • Symbolic Link: \DosDevices\BdApiUtil
    • Observable through kernel debugging or EDR kernel module APIs
    • Detection Confidence: DEFINITE (observable via Sysmon Event 6)
  3. IOCTL Communication Pattern:
    • IOCTL Code: 0x800024B4
    • Caller: rootkit.dll or secondary process
    • Destination: BdApiUtil64.sys driver
    • Observable through kernel-mode hooking or ETW tracing
    • Detection Confidence: HIGHLY LIKELY (requires kernel access)

Forensic Artifact Detection

Post-Incident Evidence:

  1. Sysmon Event ID 6 (Driver Loaded): 
    Event ID: 6 (Driver Loaded)
ImageLoaded: C:\Windows\System32\Drivers\BdApiUtil64.sys
Signed: true (Baidu signature)
SignatureStatus: Valid
TimeLoaded: [Infection Timestamp]
    • Indicates driver loading with kernel privileges
    • Baidu signature legitimate but suspicious context (BYOVD exploitation)
    • Detection Confidence: DEFINITE
  2. Sysmon Event ID 5 (Process Termination - Mass): 
    Multiple events within 60 seconds:
Event ID: 5 (Process Terminated)
TargetImage: MsMpEng.exe, NisSrv.exe, CSFalconService.exe, [20+ more]
Time Delta: <60 seconds for complete sequence
    • Indicates mass security product elimination
    • Temporal pattern specific to rootkit.dll execution
    • Detection Confidence: DEFINITE
  3. Event ID 4697 (Service Installed): 
    Service Name: Bprotect
Service File Name: C:\Windows\System32\Drivers\BdApiUtil64.sys
Service Type: Kernel driver
Start Type: Auto/System
    • Indicates rootkit.dll service registration
    • Timeline correlation with other indicators
    • Detection Confidence: DEFINITE
  4. Registry Artifacts: 
    HKLM\SYSTEM\CurrentControlSet\Services\Bprotect
HKLM\SOFTWARE\...[additional config keys]
    • Persistence configuration
    • Timeline analysis reveals infection timeframe
    • Detection Confidence: DEFINITE

Detection by Environment Type

Environments with Advanced Monitoring:

  • EDR solutions (pre-rootkit.dll execution): Detection probability HIGH
  • Kernel-mode hooking: Detection probability HIGH
  • Sysmon + SIEM correlation: Detection probability DEFINITE

Environments with Basic Monitoring:

  • Process-level monitoring (after rootkit.dll execution): Detection probability REDUCED (security products terminated)
  • File integrity monitoring: Detection probability MEDIUM (depends on timing)
  • Registry monitoring: Detection probability HIGH (service creation observable)

Post-Infection Forensic Detection:

  • Hash-based detection: Detection probability DEFINITE
  • Timeline analysis: Detection probability DEFINITE
  • Service/driver forensics: Detection probability DEFINITE

Threat Assessment

Severity Classification: CRITICAL (9.2/10)

rootkit.dll represents a CRITICAL threat to enterprise environments due to comprehensive security product neutralization and multi-vector defense evasion capabilities. This assessment reflects:

  1. Systemic Impact: Affects entire security infrastructure, not individual systems
  2. Scope: Enables undetected ransomware operations against protected environments
  3. Operational Difficulty: Requires complete system rebuild for reliable remediation
  4. Investigation Difficulty: Targets forensic tools preventing post-incident analysis

Risk Factor Breakdown

Security Product Neutralization (9.5/10 - CRITICAL):

  • 20+ security products targeted for elimination
  • Kernel-level privileges prevent resistance
  • Ring-0 access through BdApiUtil64.sys bypasses user-mode protection
  • Complete security infrastructure elimination within 60 seconds

Persistence Capability (9.0/10 - CRITICAL):

  • Kernel driver deployment survives user-mode cleanup
  • Service-based loading provides automatic restart capability
  • File hiding prevents driver detection by remediation tools
  • PowerShell integration enables re-infection through scripts

Anti-Forensics Effectiveness (8.5/10 - HIGH):

  • Targets Process Explorer, debuggers, and analysis tools
  • Prevents memory forensics via Volatility/DumpIt targeting
  • Prevents network analysis via Wireshark/Tshark targeting
  • Creates conditions where incident investigation becomes severely hampered

Analysis Tool Evasion (8.0/10 - HIGH):

  • 15+ forensic and analysis tools targeted
  • Memory dump tools disabled (prevents malware state recovery)
  • Debuggers disabled (prevents reverse engineering)
  • Network sniffers disabled (prevents C2 traffic analysis)

Detection Difficulty (7.8/10 - HIGH):

  • BYOVD driver signature is legitimate (Baidu signature valid)
  • Behavioral detection requires advanced monitoring capabilities
  • Hash-based detection effective only if sample known
  • Signature-based detection unavailable for zero-day variants

Operational Impact Assessment

Immediate Post-Execution:

  • All targeted security products cease functioning
  • File and API hooking becomes active
  • Anti-forensics begins targeting analysis tools
  • Conditions created for undetected ransomware deployment

Ransomware Stage (Following rootkit.dll):

  • Encryption operations proceed without detection
  • Ransomware file creation hidden by file hiding mechanism
  • Network C2 communication undetectable (network tools disabled)
  • Incident response capabilities severely limited

Investigation and Recovery:

  • Forensic collection tools targeted and disabled
  • Memory analysis compromised (volatility disabled)
  • Disk analysis compromised (string tools disabled)
  • Timeline reconstruction extremely difficult due to anti-forensics

Threat Actor Sophistication

rootkit.dll demonstrates PROFESSIONAL-GRADE MALWARE DEVELOPMENT indicating:

  1. Deep Windows Knowledge:
    • BYOVD exploitation technique (requires driver vulnerability knowledge)
    • Ring-0 privilege understanding
    • Kernel API familiarity
    • Service and registry manipulation
  2. Advanced Software Engineering:
    • Rust-based implementation (indicates language flexibility)
    • Modular architecture with dispatcher pattern
    • Thread-based isolation for stealth
    • Comprehensive error handling
  3. Extensive Defensive Environment Research:
    • 20+ security product targeting (requires product knowledge)
    • Forensic tool targeting (indicates incident response process understanding)
    • Attack chain optimization (indicates testing and refinement)
    • Multi-vector evasion (sophisticated threat modeling)
  4. Operational Experience:
    • Integration into larger toolkit (Arsenal-227)
    • Evolution from simpler components (killer.dll)
    • Redundancy in attack options
    • Professional infrastructure (open directory hosting)

Comparative Threat Assessment

Threat Type Comparable Sophistication Differentiation
Ransomware Gangs LockBit, BlackCat, Play Similar kernel exploitation, but rootkit.dll more defense-focused
APT Toolkits Lazarus, APT28 Professional quality, but rootkit.dll commercial ransomware focus
Crimeware Kits Standard RAT + ransomware rootkit.dll represents significant step above typical crimeware

Conclusion: rootkit.dll sophistication aligns with TOP-TIER ORGANIZED CYBERCRIME OPERATIONS with significant development resources and extensive operational experience.

Remediation Guidance

Overview: Complete System Rebuild Required (MANDATORY)

rootkit.dll necessitates COMPLETE SYSTEM REBUILD rather than targeted cleanup. This recommendation stems from the component’s kernel-level deployment, comprehensive defense neutralization, and anti-forensics capabilities that create conditions where verification of successful remediation becomes impossible.

Rebuild Rationale

Kernel-Level Deployment:

  • BdApiUtil64.sys driver operates at Ring-0 (kernel privilege level)
  • Kernel rootkits cannot be reliably removed through user-mode cleanup
  • Driver may persist through standard remediation procedures
  • Verification of successful driver removal becomes unreliable

File Hiding and API Hooking:

  • File system interception prevents reliable malware file detection
  • API hooks may hide remnants from remediation tools
  • Complete certainty of malware removal impossible without kernel analysis
  • Residual hidden files could enable re-infection

Comprehensive Defense Neutralization:

  • Systematic destruction of security products prevents re-monitoring during cleanup
  • Forensic tools disabled prevent incident investigation
  • Cleanup verification tools targeted for elimination
  • Defenders cannot verify that malware is actually removed

Anti-Forensics Interference:

  • Memory forensic tools disabled (prevents state analysis)
  • Disk forensic tools disabled (prevents artifact recovery)
  • Analysis tools disabled (prevents capability verification)
  • Creates conditions where cleanup success cannot be demonstrated

Professional-Grade Architecture:

  • Sophisticated dispatcher enables multiple evasion functions
  • Modular design allows re-infection through configuration changes
  • PowerShell integration enables script-based persistence
  • Multi-vector evasion creates residual infection risk

Rebuild Procedure

Phase 1: Immediate Response (CRITICAL - Perform Urgently)

Priority 1a: System Isolation

  • Disconnect network cable (isolate from network completely)
  • Disable wireless connectivity (if laptop)
  • Isolate from other systems physically
  • Rationale: Prevent C2 communication and lateral movement to other systems

Priority 1b: Evidence Preservation (CRITICAL - Before Any System Modification)

  • Capture full memory dump using DumpIt or forensic tool (requires USB/external drive)
    • Command: C:\DumpIt\DumpIt.exe /O C:\memory.dmp (or similar forensic tool)
    • This captures malware state for forensic analysis
  • Create full disk image using Encase, FTK, or dd equivalent
    • This preserves evidence before system modification
  • Store evidence on isolated external media (never reconnect to network)
  • Rationale: Memory dumps and disk images provide evidence for forensic analysis and legal proceedings

Priority 1c: Assessment and Notification

  • Determine infection scope
    • Timeline: When rootkit.dll was first executed
    • Affected users: Which accounts logged in during infection period
    • Network access: What network resources were accessible
  • Alert executive leadership immediately
    • System compromised at kernel level
    • Security infrastructure neutralized
    • Complete rebuild required
    • Estimated recovery timeline (see Phase 2-4)
  • Begin incident notification procedures per organizational policy
    • Regulatory notification requirements (breach notification laws)
    • Customer notification (if customer data potentially compromised)
    • Law enforcement (ransomware cases typically warrant reporting)

Phase 2: System Rebuild (CRITICAL - Perform Before Returning to Production)

Priority 2a: Wipe and Clean OS Installation (MANDATORY)

  • Boot system from trusted installation media (USB with clean Windows ISO)
  • Completely wipe hard drive (delete all partitions)
    • Command: diskpart -> list disk -> select disk X -> clean
    • This removes all traces of infection including kernel-level components
  • Create single partition and format as NTFS
  • Install clean operating system from trusted source
    • Use original media or validated ISO (hash-verified)
    • Install to fresh system partition only
    • Do NOT restore from backup (backups may contain malware)

Priority 2b: Security Updates and Hardening

  • Update operating system with latest security patches
    • Install all Windows updates before network connection
    • Install critical security patches for pre-existing vulnerabilities
  • Deploy Vulnerable Driver Blocklist (Microsoft)
    • Windows 11 with HVCI: Automatically blocks vulnerable drivers
    • Windows 10: Manual configuration of driver blocklist required
    • Goal: Prevent future BYOVD exploitation (same attack vector)
  • Configure Windows Defender with enhanced settings
    • Enable real-time protection
    • Enable tamper protection (prevents defense evasion)
    • Enable cloud-delivered protection
  • Install latest security product (EDR solution)
    • Deploy EDR agent with kernel-mode driver
    • Enable behavioral monitoring
    • Enable advanced threat detection

Priority 2c: Data Restoration

  • Restore user data from pre-infection backup
    • Use backups created BEFORE suspected infection date
    • Scan restored data with security tools before user access
    • Be aware: Ransomware encrypted files may have been backed up
  • Restore critical business data from clean sources
    • Verify data integrity before restoration
    • Use versioning systems for application data when possible

Phase 3: Verification and Testing (CRITICAL - Ensure Successful Rebuild)

Priority 3a: System Verification

  • Verify clean OS installation with baseline tools
    • Run Windows Update to verify no pending updates
    • Check Device Manager for unexpected devices (should see only expected hardware)
    • Verify Service list does NOT include Bprotect service (key indicator of residual rootkit.dll)
  • Verify security product functionality
    • Confirm EDR agent is running and communicating with server
    • Verify antivirus engine is running and up-to-date
    • Test with EICAR test file to verify detection working
  • Verify forensic tool functionality
    • Confirm Process Explorer launches and shows processes
    • Confirm Wireshark captures network traffic
    • Confirm memory dump tools function correctly
    • Rationale: If these tools had been disabled by rootkit.dll, they should now work

Priority 3b: Timeline Reconstruction

  • Analyze preserved forensic images to understand infection timeline
    • Determine exact execution time of rootkit.dll
    • Identify how threat actor gained access (initial compromise)
    • Identify follow-on payloads deployed (ransomware, C2)
    • Identify data potentially accessed or exfiltrated
  • Reconstruct attacker activities from logs
    • Review Security Event logs for authentication patterns
    • Review Application logs for relevant events
    • Interview users about suspicious activities observed
  • Estimate damage and recovery scope
    • How many files encrypted (if ransomware executed)
    • What systems in network were compromised
    • How much data could have been exfiltrated

Phase 4: Enhanced Monitoring and Hardening (CRITICAL - Prevent Recurrence)

Priority 4a: Post-Rebuild Monitoring (30-Day Period)

  • Deploy enhanced EDR rules for Arsenal-227 toolkit indicators
    • Alert on rundll32.exe execution with suspicious DLLs
    • Alert on mass process termination (20+ processes in 60 seconds)
    • Alert on BdApiUtil64.sys driver loading
    • Alert on Bprotect service creation
  • Monitor for re-infection attempts
    • Watch for rootkit.dll hash matches
    • Watch for similar BYOVD exploitation patterns
    • Watch for security product termination events
    • Watch for PowerShell-based attack patterns
  • Verify backup restoration integrity
    • Spot-check restored files for modification dates
    • Verify application databases not corrupted
    • Verify business continuity procedures working correctly

Priority 4b: Vulnerability Remediation

  • Block vulnerable driver exploitation
    • If Windows 11: Verify HVCI enabled and driver blocklist active
    • If Windows 10: Manually add vulnerable drivers to blocklist
    • Review all deployed drivers for known vulnerabilities
  • Patch initial compromise vector
    • If phishing: Reinforce user awareness training
    • If web vulnerability: Patch vulnerable application
    • If credential compromise: Rotate all credentials and enable MFA

Priority 4c: Defense Infrastructure Review

  • Evaluate adequacy of security monitoring
    • Verify EDR agent deployment on all systems
    • Verify antivirus coverage on all systems
    • Verify SIEM/logging infrastructure for detection capability
  • Implement detective controls for future BYOVD attacks
    • Kernel-mode monitoring for driver loading
    • Behavioral detection for process termination patterns
    • File system monitoring for hidden file creation
  • Establish incident response procedures
    • Pre-define escalation procedures for kernel-level attacks
    • Establish forensic collection procedures
    • Establish communication protocols for security incidents

Remediation Success Criteria

System is Considered Remediated When:

  1. Clean OS installation confirmed (no Bprotect service present)
  2. All security products functioning normally
  3. All forensic tools operational
  4. Evidence collection and analysis complete
  5. Post-recovery monitoring active for 30 days without incident
  6. Defensive gaps identified and remediation planned

System Should Return to Production When:

  1. All above criteria met
  2. 30-day enhanced monitoring period complete
  3. Backup and disaster recovery procedures tested
  4. User acceptance testing confirms business functionality
  5. All stakeholder sign-offs obtained

Response Priorities

rootkit.dll requires prioritized response reflecting the critical nature of kernel-level compromise and systematic defense neutralization.

Priority 1: CRITICAL - Immediate System Isolation

Action: Disconnect Infected System from Network Immediately

All systems with confirmed rootkit.dll execution must be isolated from network access within minutes of detection:

  • Physical network cable disconnection (primary method)
  • Wireless connectivity disabled (for laptops)
  • VPN/remote access credentials revoked
  • Network access controls (802.1X) disabling account
  • Firewall rules blocking network access

Rationale:

  • Prevent C2 communication with threat actor infrastructure
  • Prevent lateral movement to other network systems
  • Prevent ransomware payload deployment to network shares
  • Contain incident scope to single system

Success Indicator: System cannot establish network connectivity despite administrative attempts to connect

Priority 2: CRITICAL - Evidence Preservation

Action: Capture Full Memory Dump and Disk Image Before System Modification

Forensic preservation must occur immediately after isolation, before any remediation attempts:

  • Full memory dump (preserves malware state and Ring-0 components)
  • Complete disk image (preserves file system including hidden files)
  • Event log preservation (captures timeline information)
  • Network session documentation (captures C2 connections)

Rationale:

  • Malware in memory contains behavioral evidence
  • Kernel drivers may hide from post-execution analysis
  • Forensic images provide evidence for investigation and legal proceedings
  • Ring-0 components may be impossible to analyze after system restart

Success Indicator: Evidence media created and stored safely with chain of custody documentation

Priority 3: CRITICAL - Threat Scope Assessment

Action: Determine Infection Timeline and Impact Scope Urgently

While evidence is being preserved, begin assessment of how extensive the compromise is:

  • Infection timeline (when rootkit.dll executed)
  • Affected systems (which computers in network had rootkit.dll)
  • Affected users (which user accounts had access)
  • Data access scope (what systems/data were accessible from infected system)
  • Ransomware execution (did ransomware payload deploy; how many files encrypted)

Rationale:

  • Identify all affected systems requiring rebuild
  • Determine urgency of notification and recovery
  • Establish scope of potential data breach
  • Inform rebuild prioritization and sequence

Success Indicator: Clear understanding of infection scope and affected systems documented

Priority 4: URGENT - System Rebuild Initiation

Action: Begin Complete System Rebuild as Soon as Evidence Preserved

Once forensic evidence collected, initiate full system wipe and clean OS installation:

  • Boot from clean installation media
  • Wipe hard drive completely
  • Install clean operating system
  • Apply security updates and patches
  • Deploy security tools (EDR, antivirus)
  • Restore user data from pre-infection backup

Rationale:

  • Kernel-level rootkits cannot be reliably cleaned through targeted remediation
  • File hiding and API hooking prevent verification of cleanup
  • Complete rebuild provides certainty of malware removal
  • Timing is critical to restore business operations

Success Indicator: Clean system operational and verified through security tool functionality testing

Priority 5: URGENT - Credential Rotation

Action: Reset All Credentials for Affected Systems Urgently

Kernel-level compromise enables credential harvesting from memory:

  • Reset all passwords for accounts that logged into compromised system
  • Enable multi-factor authentication (MFA) on all accounts
  • Rotate API keys and service account credentials
  • Reset SSH keys if applicable
  • Reset application tokens and access credentials

Rationale:

  • rootkit.dll with Ring-0 access can harvest credentials from memory
  • Threat actor may have obtained credentials enabling lateral movement
  • Credential compromise may not be obvious from post-event analysis
  • Defensive measure even if credential theft not confirmed

Success Indicator: All credentials changed and MFA enabled on affected user accounts

Priority 6: URGENT - Follow-On Artifact Hunting

Action: Conduct Network-Wide Threat Hunt for Arsenal-227 Toolkit Components

While rebuilding systems, conduct proactive hunting for related toolkit components:

  • Hunt for killer.dll samples (basic BYOVD-based termination)
  • Hunt for nethost.dll samples (C2 communication)
  • Hunt for enc_*.exe samples (ransomware payloads)
  • Hunt for BdApiUtil64.sys driver (embedded in multiple components)
  • Hunt for lpe.exe samples (privilege escalation wrapper)

Rationale:

  • Arsenal-227 components often deployed together
  • Identifying follow-on payloads prevents additional attacks
  • Early detection prevents ransomware encryption
  • Comprehensive threat hunting prevents recurrence

Detection Methods:

  • File hash searches (IOC-based detection)
  • Behavioral pattern detection (mass process termination)
  • Service/driver detection (Bprotect service, BdApiUtil64.sys)
  • Timeline correlation (rootkit.dll execution pattern)

Success Indicator: Comprehensive threat hunt completed; all Arsenal-227 components identified and remediated

Priority 7: Ongoing - Enhanced Monitoring

Action: Implement Enhanced Detection Rules for Arsenal-237 Toolkit (30-Day Minimum)

Deploy specialized detection rules post-rebuild to identify any re-infection attempts:

  • Process Termination Events: Alert on rapid termination of security products
  • Driver Loading Events: Alert on BdApiUtil64.sys or similar vulnerable drivers
  • Service Creation Events: Alert on Bprotect or similar suspicious service creation
  • rundll32.exe Alerts: Alert on suspicious DLL execution via rundll32
  • PowerShell Pattern Matching: Alert on obfuscated PowerShell execution

Rationale:

  • Arsenal-227 threat actors may attempt re-infection
  • Enhanced monitoring provides rapid detection of recurrence
  • 30-day enhanced period addresses typical dwell time between compromise and detection
  • Early detection enables faster containment

Duration: Maintain enhanced monitoring rules for minimum 30 days; consider permanent deployment for high-value systems

Key Takeaways

1. rootkit.dll is NOT a Traditional Rootkit

The component named “rootkit.dll” is fundamentally different from what the name suggests. This is an Advanced Defense Evasion Framework that weaponizes legitimate but vulnerable drivers (Baidu antivirus) rather than implementing kernel-mode process hiding. Understanding this distinction prevents mischaracterization of the threat’s actual capabilities and appropriate defense prioritization.

2. Comprehensive Defense Neutralization Creates Complete Blindness

The systematic elimination of 20+ security products (both mainstream vendors and EDR solutions) creates conditions where defenders lose complete visibility into subsequent attack stages. This is not selective targeting of a single vendor-this is architectural neutralization of the entire defensive infrastructure, enabling undetected ransomware operations.

3. Kernel-Level Compromise Mandates Complete System Rebuild

The embedded BdApiUtil64.sys driver deployment at Ring-0 (kernel privilege level) means that targeted cleanup is impossible. Kernel rootkits cannot be reliably removed through user-mode remediation. Complete system rebuild is not conservative-it is the only reliable remediation method. Any attempt at targeted cleanup leaves residual infection risk.

4. Reflects Professional-Grade Threat Actor Operations

rootkit.dll’s sophisticated modular architecture, comprehensive targeting, anti-forensics capabilities, and integration into larger Arsenal-227 toolkit demonstrates TOP-TIER ORGANIZED CYBERCRIME OPERATIONS with significant development resources. This is not amateur malware-this represents professional software engineering applied to attack infrastructure.

5. Evolution from Basic BYOVD to Comprehensive Framework Shows Threat Maturation

The progression from killer.dll (simple BYOVD-based termination) to rootkit.dll (multi-vector evasion framework) shows threat actors learning from initial deployments and refining attack techniques. This represents threat actor optimization over time, suggesting continued attacks and further toolkit refinement.

6. File Hiding and API Hooking Create Persistent Stealth Layer

Beyond process termination, rootkit.dll implements file system stealth and API hooking mechanisms that provide persistent concealment of malware files and network activity. This differs fundamentally from temporary defense neutralization and explains why rebuilding is essential-the stealth mechanisms persist even if security products are restored.

7. Anti-Forensics Targeting Prevents Post-Incident Investigation

The systematic targeting of forensic tools (memory dump, disk imaging, analysis tools) means that incident investigation becomes extremely difficult. Defenders cannot verify remediation success or understand the full scope of the compromise. This anti-forensics capability has implications for recovery confidence and incident understanding.

8. Multi-Product Targeting Prevents Backup Reliance

Organizations cannot rely on individual security products as backup detection sources when the toolkit targets ALL major vendors. The diversity of targeting means that organizational detection posture depends on advanced detection methods, not product redundancy. This has implications for security architecture decisions.

9. PowerShell Integration Enables Flexible Attack Execution

The PowerShell integration capability means rootkit.dll serves as a foundation for script-based attacks executed with SYSTEM privileges and in an environment with neutralized defenses. This flexibility allows threat actors to adapt attack execution to specific environments without releasing new malware variants.

10. Arsenal-227 Represents Significant Operational Capability

The comprehensive toolkit (privilege escalation, defense evasion, C2, ransomware) discovered on an open directory indicates that Arsenal-227 threat actors have significant operational capability and confidence in their infrastructure. The open directory hosting suggests either misconfiguration or intentional exposure, both indicating threat actor activity ongoing without significant fear of law enforcement disruption.

Indicators of Compromise

File Hashes

Hash Type Value
SHA256 e71240f26af1052172b5864cdddb78fcb990d7a96d53b7d22d19f5dfccdf9012
SHA1 483feeb4e391ae64a7d54637ea71d43a17d83c71
MD5 674795d4d4ec09372904704633ea0d86

File Metadata

Property Value
Filename rootkit.dll
File Size 413,696 bytes (404 KB)
File Type PE64 DLL
Architecture x64
Compiler Rust (rustc)
Signature Unsigned

Driver Indicators

Indicator Value
Driver Name BdApiUtil64.sys
Device Object \Device\BdApiUtil
Symbolic Link \DosDevices\BdApiUtil
Service Name Bprotect
IOCTL Code 0x800024B4
Driver Version Baidu Antivirus v5.0.3.84333

Execution Indicators

Indicator Type Values
Process Name rundll32.exe
Command Line Pattern rundll32.exe [path]\rootkit.dll
Parent Process lpe.exe or alternative privilege escalation tool
Execution Privilege SYSTEM (post-privilege-escalation)

Service and Registry Indicators

Path Values
Service Registry HKLM\SYSTEM\CurrentControlSet\Services\Bprotect
Service Type Kernel driver (REG_DWORD Type = 1)
Service Start Auto/System (REG_DWORD Start = 2)
ImagePath %SystemRoot%\System32\Drivers\BdApiUtil64.sys

Behavioral Indicators

Behavior Detection Method
Mass process termination (20+ security products within 60 seconds) Sysmon Event ID 5, EDR process termination events
BdApiUtil64.sys driver loading Sysmon Event ID 6, Kernel-mode monitoring
Bprotect service creation Registry monitoring, Event ID 4697
rundll32.exe execution with suspicious DLLs Process execution monitoring, command-line analysis
Unicode string manipulation for file hiding Memory analysis, API hooking detection
PowerShell script execution at SYSTEM privilege PowerShell logging, script block logging

Network Indicators

C2 Infrastructure (Arsenal-237 Discovery Location):

  • IP Address: 109.230.231.37
  • Protocol: HTTP/HTTPS
  • Port: [Common C2 ports - 443, 8080, 8443]
  • Purpose: Toolkit distribution, C2 communication

License

(c) 2026 Threat Intelligence Team. All rights reserved. Free to read, but reuse requires written permission.