Open Directory Investigation: This ransomware family was discovered on an open directory hosted at IP address 109.230.231.37, representing the “Arsenal-237” malware development toolkit. The presence of 10 ransomware variants (5 encryptors, 5 decryptors) alongside espionage tools indicates a sophisticated threat actor’s development environment. To see all other reports from this investigation see Arsenal-237 Executive Overview

Campaign Identifier: Arsenal-237-109.230.231.37-Malware-Repository

Last Updated: January 18, 2026

BLUF (Bottom Line Up Front)

Executive Summary

Business Impact Summary

The enc/dec ransomware family is a CRITICAL-severity ransomware toolkit discovered in a professional malware development repository. The ransomware employs custom-developed hybrid RSA-2048 + ChaCha20 cryptography with professional-grade performance optimization using AVX-512/AVX2/SSE CPU instructions. Analysis of 10 variants (5 encryptors, 5 decryptors) through extensive reverse engineering reveals a sophisticated development environment with versioned builds, quality assurance testing utilities, and per-victim key generation capabilities. The malware was discovered alongside espionage tools (PoetRAT malware samples) in the same repository, indicating potential dual-purpose operational use (intelligence collection + financial extortion).

The malware systematically deletes Volume Shadow Copies to prevent system restore, encrypts all accessible local drives (A-Z enumeration) and network shares, and implements multi-layered anti-analysis techniques that successfully defeated automated sandbox analysis. The cryptographic implementation is mathematically unbreakable without the threat actor’s master RSA-2048 private key and decryption password. Offline backup restoration is the only viable recovery method - decryption without the attacker’s key is computationally infeasible.

Key Risk Factors

Risk Factor	Score	Business Impact
Overall Risk	9.5/10	CRITICAL - Professional ransomware development
Data Loss Risk	10/10	Complete encryption of all local drives + network shares
Recovery Difficulty	10/10	Mathematically unbreakable encryption + VSS deletion
Cryptographic Strength	10/10	Custom RSA-2048 + ChaCha20 (banking-grade implementation)
Evasion Capability	9/10	Multi-layer anti-analysis defeated sandbox analysis
Operational Disruption	9/10	Hardware-optimized encryption (minutes to encrypt TB of data)
Development Sophistication	9/10	Professional development with versioned builds and QA testing

Recommended Actions

BLOCK infrastructure 109.230.231.37 at network perimeter immediately
DEPLOY enc/dec ransomware YARA signatures for detection across all endpoints
HUNT enterprise-wide for related malware tools (agent.exe, steal_browser.exe)
SECURE offline backups with immutable storage and air-gap isolation
HARDEN VSS deletion controls via AppLocker/WDAC restrictions
ROTATE credentials if related espionage tools detected (assume compromise)
TEST backup restoration procedures to validate recovery capabilities

Quick Reference
File Identification
Executive Technical Summary
Deep Technical Analysis
Dynamic Sandbox Analysis
MITRE ATT&CK Mapping
Frequently Asked Questions
IOCs
Detections

Quick Reference

Detections & IOCs:

Critical Infrastructure:

Distribution/C2: 109.230.231.37 (BLOCK ALL TRAFFIC)

Development Characteristics:

Sophistication: Professional malware development environment

File Identification

Encryption Variants (5 Total)

1. enc_v2.exe (PRIMARY ANALYSIS SAMPLE)

SHA256: d942896e56eb6dc83c8788c92e6fe7c57ee419b9b092f3089c74b3f0e181b154
SHA1: 60654d763e8918a10a5df9eb65b2676bd4e2a85d
MD5: 59011f6a6c53f79b9d63d53b3ea7c251
File Size: Unknown (estimated 15-20 MB)
Type: PE32+ executable, Rust-compiled
Analysis Level: FULL REVERSE ENGINEERING
Key Features: Custom ChaCha20 with AVX optimization, multi-layer anti-analysis, VSS deletion

2. enc_pervictim.exe (REVERSE ENGINEERED)

SHA256: e25e19888d615b9fb15da4cd7c4cd34dfa53250becff3d621c59c9fa38efdcf3
SHA1: c2d6e40976b237b8f0a034d30df9e60a7771c416
MD5: e2cbe3bc77b1ce11192fd0d542d6123a
File Size: Unknown (estimated 15-20 MB)
Analysis Level: FULL REVERSE ENGINEERING
Key Features: Per-victim key generation, runtime CPU dispatcher (AVX-512/AVX2/SSE), debug artifact: chacha20_pervictim.rs

3. updated_enc.exe (REVERSE ENGINEERED)

SHA256: 9cf27311a39f4915ef1ea36f101381c4b3b7fe0eeea43a9739df15c06a563651
SHA1: 45714cf92b5820ca115568d8f4ea48293dcc66b6
MD5: 91874b34526a38f9ca0727f323c3188a
File Size: Unknown (estimated 15-20 MB)
Analysis Level: FULL REVERSE ENGINEERING
Key Features: Evolutionary variant of enc_v2.exe, identical anti-debugging loops, ransom note: README.txt

4. enc.exe (AUTOMATED ANALYSIS)

SHA256: 93c53ebc8d1ee19dad41cfb7989ed047136cd80669ec8ba7b0af4016f9123cc1
SHA1: ebad3ae916e075c119c1630f007e05fa5ce8cb6f
MD5: f6b678886d38dda59678e5422697aaee
File Size: 15.8 MB
Analysis Level: Automated static analysis
Key Features: Earlier version in development timeline, basic encryption functionality

5. test_gui_enc_v2.exe (AUTOMATED ANALYSIS)

SHA256: 6c21c70ae517ccf548ac326ac133337b8d12200658ffba5a1f2d7053a34aadc6
SHA1: 426a4740043780ff152ffd651a2abb7a8692f8e3
MD5: 4ce7f0bda1f3606270e5f9677d526771
File Size: Unknown
Analysis Level: Automated static analysis
Key Features: Testing variant with GUI components, Version 2 architecture, development/QA build

Decryption Variants (5 Total)

1. dec.exe (PRIMARY ANALYSIS SAMPLE - REVERSE ENGINEERED)

SHA256: 2e6220c3ed90261bd9f0d30cc3684e7c3f763ce524fe7ff49de7bf92870031e9
SHA1: 575e763b941f74ef329e37715c46fac45abb3985
MD5: 0ad2f5880d34e9f231a28f0c0cad015b
File Size: 2.1 MB
Analysis Level: FULL REVERSE ENGINEERING
Key Features: Command-line utility (–pass, –file, –folder), PBKDF2 key derivation, RSA private key unwrapping, ChaCha20-Poly1305 AEAD decryption

2. dec_fast.exe (AUTOMATED ANALYSIS)

SHA256: 62459f33fd9a933799857e537cb3fbfd41b32658cde2a5119cc5a819aecc53ca
SHA1: 4490d9be948dbb8bc0b58c551c28bfb182a54d8a
MD5: 9e492a9e4906946c20ae061fa29e62e5
File Size: Unknown
Key Features: Performance-optimized decryption variant

3. dec_pc3.exe (AUTOMATED ANALYSIS)

SHA256: 1252b4a85ea6d33651bbcee4708f0ec14d5915f7ebe9c8de0ffb5bfc6ad8f412
SHA1: 7b7db113669abe951b5298f5a17d9fa4c2e0b84f
MD5: dddf209542b4cc9ab4f312eb46876aa9
File Size: Unknown
Key Features: Specialized decryption variant (possibly machine-specific)

4. dec_unique.exe (AUTOMATED ANALYSIS)

SHA256: 353800a0934e6de5d02f660fcde2be3e3b3d3bb70bcff3a157355c77a75cb935
SHA1: e60ee8e9516b1d9595d026c0ae84d3f93db0765e
MD5: 7581ba60eb121a0ca0499a8fe8c3bdc9
File Size: Unknown
Key Features: Variant with unique decryption parameters

5. test_decryptor.exe (AUTOMATED ANALYSIS)

SHA256: 4a41291979ce387fd5470ad5afd9db2938669d813f7da7f43dd9f53413457399
SHA1: bced673ab0cf6f008264c763f399899471d30a53
MD5: 3b53bd591f29e0a2cc3d500db4c4cf8a
File Size: Unknown
Key Features: Testing/QA decryption utility, development build

Discovery Context

This ransomware family was discovered as part of a broader malware toolkit on an exposed open directory at IP address 109.230.231.37 in December 2025. The directory contained 38 malicious executables representing a sophisticated development and testing environment, including various espionage tools, commodity RATs, persistence mechanisms, and this custom ransomware family.

Executive Technical Summary

Business Context

The enc/dec ransomware family represents a professional-grade cyber weapon with indicators of sophisticated development practices. The discovery of this ransomware alongside PoetRAT espionage tools (agent.exe, steal_browser.exe) in the same development repository suggests a comprehensive malware toolkit supporting multiple operational objectives.

The malware’s design prioritizes maximum operational impact through strong cryptography, hardware-optimized performance, and comprehensive system recovery inhibition. The presence of extensive R&D artifacts (versioned builds, testing utilities, specialized variants) indicates ongoing development by a professional team with cryptographic engineering expertise.

Key Business Impacts

Total Data Loss: Complete encryption of all accessible data (local drives A-Z + network shares) with mathematically unbreakable cryptography
Recovery Elimination: Systematic Volume Shadow Copy deletion forces reliance on offline backups
Rapid Encryption: Hardware-optimized ChaCha20 (AVX-512) can encrypt hundreds of gigabytes in minutes
Dual Threat Model: Repository contains both espionage tools (PoetRAT malware samples) and ransomware, indicating potential data exfiltration before encryption
Regulatory Exposure: Data encryption creates potential GDPR, HIPAA, PCI-DSS breach notification requirements

Detection Challenges

Custom Cryptography: Hand-coded ChaCha20 implementation defeats library-based detection signatures
Successful Sandbox Evasion: Multi-layer anti-analysis techniques (stack-checking, VEH, Sleep() calls) prevented automated behavioral analysis
Professional Development: Extensive obfuscation, runtime hardware optimization, and anti-debugging create significant reverse engineering barriers
High Sophistication: Custom cryptographic engineering requires specialized analysis capabilities beyond commodity malware

Executive Risk Assessment

CRITICAL RISK - The enc/dec ransomware family’s combination of professional development practices, mathematically unbreakable encryption, comprehensive recovery inhibition, and dual-purpose operational model (espionage + extortion) creates catastrophic risk for unprepared organizations. Industry data shows 60% of small businesses close within 6 months of major cyberattacks. The only reliable defense is offline, immutable, tested backup infrastructure - decryption without the attacker’s key is impossible.

Deep Technical Analysis

Execution Flow Overview

The enc/dec ransomware family follows a sophisticated multi-stage execution model designed to evade analysis while maximizing encryption speed and system impact.

Encryption Workflow (enc_v2.exe Reference Model)

1. Entry Point (_start @ 0x1400013f0)
   |
2. Anti-Analysis Initialization (sub_140001180)
   | - Stack base monitoring loop (debugger detection)
   | - SetUnhandledExceptionFilter installation
   | - Sleep(1000ms) on debugger detection
   |
3. Obfuscated Dispatch Chain (main -> sub_1400c5b10 -> sub_140003d98)
   | - AddVectoredExceptionHandler installation
   | - Multi-layer function wrappers
   | - Deliberate call graph obfuscation
   |
4. Core Ransomware Payload (sub_1400087d4)
   | - Print: "[*] Using RSA+ChaCha20 encryption"
   | - Execute VSS deletion commands
   | - Enumerate drives A-Z
   | - Network share discovery (netuse module)
   |
5. Cryptographic Dispatcher (sub_14012e430)
   | - Block size analysis
   | - Route to appropriate crypto handler
   |
6. Custom ChaCha20 Engine (sub_140131680)
   | - AVX-optimized ARX operations
   | - Per-file session key encryption
   | - File content XOR with keystream

Decryption Workflow (dec.exe Reference Model)

1. Entry Point + Anti-Analysis (sub_140001180)
   | - Identical stack-checking loop
   |
2. Argument Parsing (sub_14000a1a4)
   | - Parse --pass, --file, --folder flags
   | - Load blocklists (folders, extensions, services)
   |
3. Key Derivation Ceremony (sub_1400032e2)
   | - User password -> PBKDF2 -> symmetric key
   | - Symmetric key -> decrypt embedded RSA private key
   | - RSA private key -> decrypt per-file session key
   |
4. File Decryption (sub_1400088d8)
   | - Read encrypted session key from file footer
   | - ChaCha20-Poly1305 decryption (sub_140002d86)
   | - "expand 32-byte k" constant validation
   | - Poly1305 authentication tag verification
   |
5. Cleanup Operations
   | - Delete README_FOR_DECRYPT.txt ransom notes
   | - Terminate ransom_note_exec.exe process

Executive Technical Context

What This Means: The methodical execution flow demonstrates professional software engineering with clear separation of concerns: anti-analysis initialization, obfuscated dispatch, cryptographic operations, and system impact functions. The dual-mechanism approach (encryption + VSS deletion) creates defense-in-depth for the attacker, ensuring data inaccessibility even if one recovery method survives.

Business Impact: The systematic approach maximizes operational damage while minimizing detection opportunities. Organizations face complete data loss with no viable recovery path except offline backups.

Detection Strategy: Focus on the initialization phase (stack-checking loops) and system impact operations (VSS deletion commands) as high-confidence detection points. Cryptographic operations alone provide limited detection value due to custom implementation.

Cryptographic Architecture

The ransomware employs a hybrid encryption scheme combining asymmetric and symmetric cryptography with custom implementations demonstrating exceptional technical sophistication.

Hybrid Encryption Workflow

[MASTER KEY HIERARCHY]

Threat Actor Master RSA-2048 Private Key (offline, attacker-controlled)
         |
Threat Actor Master RSA-2048 Public Key (embedded in encryptor executables)
         |
Per-File ChaCha20 Session Key (256-bit, randomly generated for each file)
         |
File Data Encryption (ChaCha20 stream cipher, hardware-optimized)

Encryption Process

Phase 1: Key Generation (Per File)

Generate random 256-bit ChaCha20 session key
Encrypt session key with embedded RSA-2048 public key
Store encrypted session key in file footer

Phase 2: File Encryption

Read plaintext file contents into memory
Generate ChaCha20 keystream from session key + nonce
XOR plaintext with keystream (encryption)
Overwrite original file with encrypted data + encrypted session key footer

Phase 3: Decryption Requirements (Attacker-Controlled)

User must provide correct password (–pass parameter)
Password -> PBKDF2 -> derives key to decrypt RSA private key embedded in dec.exe
Decrypted RSA private key -> decrypt per-file session key from file footer
Session key + nonce -> generate ChaCha20 keystream
XOR encrypted data with keystream (decryption)

Cryptographic Strength Assessment

RSA-2048 Analysis:

Key size: 2048 bits (industry standard for government/military)
Cryptanalysis requirement: Billions of years of supercomputer time with current technology
No known mathematical weaknesses in RSA algorithm
NIST-approved algorithm for classified information protection

ChaCha20 Analysis:

Algorithm designer: Daniel J. Bernstein (renowned cryptographer)
Key size: 256 bits (maximum security level)
Industry usage: Google, Cloudflare, Signal, OpenVPN
Cryptographic strength: Equivalent to AES-256 (banking-grade)
Arsenal-237 implementation: Custom hand-coded (NOT vulnerable library versions)

Reverse Engineering Assessment:

No cryptographic weaknesses identified during deep technical analysis
Implementation follows RFC 8439 specification correctly
Professional-grade code quality with proper AEAD (Authenticated Encryption with Associated Data)
Poly1305 authentication prevents tampering attacks

Executive Technical Context

What This Means: The hybrid cryptographic architecture combines the mathematical strength of RSA-2048 for key protection with the performance efficiency of ChaCha20 for file encryption. This design pattern is identical to industry-standard secure communications protocols (TLS, Signal).

Business Impact for Recovery: Without the threat actor’s master RSA-2048 private key and decryption password, file recovery is mathematically impossible. Industry data shows 35% of ransom-paying organizations do not receive functional decryption tools. Offline backup restoration is the only cryptographically-independent recovery method.

Detection Implications: The custom ChaCha20 implementation (not library-based) defeats signature-based cryptographic API monitoring. Detection must focus on file system behavior (mass encryption operations) rather than cryptographic function calls.

Custom ChaCha20 Implementation

CRITICAL FINDING: The ChaCha20 implementation is NOT based on standard cryptographic libraries (OpenSSL, libsodium, Windows CryptoAPI). It is a completely custom, hand-coded implementation featuring professional-grade performance engineering.

ChaCha20 Identification Evidence

// From enc_v2.exe (sub_140131680) and dec.exe (sub_140002d86)
// The definitive "smoking gun" for ChaCha20:

__builtin_strncpy(dest: &var_5d0, src: "expand 32-byte k", count: 0x40)

This exact 16-byte constant is specified in RFC 8439 (ChaCha20 and Poly1305 for IETF Protocols) and is the initialization constant for the ChaCha20 state matrix. Its presence definitively identifies the algorithm.

ARX (Add-Rotate-XOR) Core Operations

// From enc_v2.exe (sub_140131680)
// ChaCha20 quarter-round ARX pattern

zmm7 = _mm_srli_epi64(zmm3 ^ arg3, 7);          // XOR + Rotate
zmm3 = _mm_add_epi64(                           // Add
    (_mm_srli_epi64(zmm3, 6) | zmm7) & zmm1,    // Rotate + Mask
    zmm4                                         // Add
);

These vectorized operations implement the ChaCha20 quarter-round using AVX SIMD instructions for maximum parallelism.

Technical Significance: The assembly code pattern of Add-Rotate-XOR operations is unique to ChaCha20’s quarter-round function. This exact sequence doesn’t appear in AES, Salsa20, or other ciphers - it serves as a definitive cryptographic fingerprint.

Runtime Hardware Optimization (enc_pervictim.exe)

The enc_pervictim.exe variant features a sophisticated runtime CPU dispatcher that detects hardware capabilities and selects the optimal implementation:

CPU Feature Detection Process:

Check for AVX-512 instruction set support
Check for AVX2 instruction set support
Check for SSE instruction set support (fallback)

Implementation Selection:

AVX-512 Path: Use 512-bit ZMM registers (16 parallel operations)
AVX2 Path: Use 256-bit YMM registers (8 parallel operations)
SSE Path: Use 128-bit XMM registers (4 parallel operations)

Performance Impact:

AVX-512 can encrypt data 4x faster than SSE fallback
Modern server CPUs with AVX-512 support enable encryption of hundreds of gigabytes in minutes
Creates extremely short detection window (minutes to encrypt entire organization)

Executive Technical Context

What This Means: SIMD (Single Instruction Multiple Data) optimization is analogous to a factory assembly line - instead of encrypting files one at a time sequentially, the malware processes multiple files simultaneously in parallel. This level of performance engineering requires:

Deep understanding of ChaCha20 algorithm internals
Expertise in x86-64 SIMD instruction sets (AVX-512/AVX2/SSE)
Low-level performance optimization skills
Custom compiler intrinsics knowledge

Business Impact: Hardware-optimized encryption enables attackers to encrypt entire enterprise file servers in minutes rather than hours. This dramatically reduces detection and response windows. Organizations must assume rapid, organization-wide encryption upon initial compromise.

Conclusion: This is NOT the work of commodity ransomware developers. This indicates a professional development team with specialized cryptographic engineering capabilities.

Anti-Analysis Techniques

The ransomware family employs multiple redundant anti-analysis techniques creating a layered defense against reverse engineering.

Signature 1: Stack-Based Anti-Debugging Loop

Present in ALL analyzed samples (enc_v2.exe, updated_enc.exe, enc_pervictim.exe, dec.exe):

// From sub_140001180 (C runtime initialization)

void* StackBase = gsbase->NtTib.Self->NtTib.StackBase;

if (0 == data_140208570)
    data_140208570 = StackBase;  // Store initial stack base

while (true) {
    if (StackBase != rax_1) {    // Detect stack base changes
        Sleep(0x3e8);             // Sleep 1 second (sandbox evasion)
        continue;                 // Loop indefinitely
    }
    // Normal execution continues...
}

Purpose:

Detect debugger attachment (stack base can change during debugging)
Evade automated sandboxes (Sleep calls slow analysis)
Force manual analysis to be extremely time-consuming

Signature 2: Vectored Exception Handling (VEH)

Present in encryption variants (enc_v2.exe, updated_enc.exe, enc_pervictim.exe):

// From dispatcher functions (sub_1400c5b10, sub_1400c5db0, sub_1400c6d50)

AddVectoredExceptionHandler(0, sub_1400e92c0);  // enc_v2.exe
AddVectoredExceptionHandler(0, sub_1400e9560);  // updated_enc.exe
AddVectoredExceptionHandler(0, sub_1400ea500);  // enc_pervictim.exe

Purpose:

Intercept exceptions before standard debuggers can handle them
Interfere with breakpoint-based debugging
More sophisticated than standard SEH (Structured Exception Handling)

Signature 3: Obfuscated Execution Flow

All variants use multi-layer function wrappers to obscure the true execution path:

main() -> dispatcher1() -> dispatcher2() -> dispatcher3() -> payload()

Each dispatcher passes function pointers to the next stage, making static call graph analysis extremely difficult.

Signature 4: Unhandled Exception Filter

// From C runtime (sub_140001180)

SetUnhandledExceptionFilter(sub_140141e20);

Installs custom handler to catch and process unhandled exceptions, preventing crash dumps that could aid analysis.

Comparative Analysis

Anti-Analysis Technique	enc_v2.exe	updated_enc.exe	enc_pervictim.exe	dec.exe
Stack-checking loop	PRESENT	PRESENT	PRESENT	PRESENT
VEH installation	PRESENT	PRESENT	PRESENT	ABSENT
UEF installation	PRESENT	PRESENT	PRESENT	PRESENT
Sleep() evasion	PRESENT	PRESENT	PRESENT	PRESENT
Obfuscated dispatch	PRESENT	PRESENT	PRESENT	PRESENT

Executive Technical Context

What This Means: These shared signatures provide high-confidence attribution to a single threat actor and enable robust YARA rule creation for detection. The consistency across variants indicates systematic engineering practices and code reuse.

Business Impact: Multi-layer anti-analysis defeats automated sandbox analysis and significantly increases reverse engineering costs. Organizations cannot rely on standard malware analysis platforms for behavioral detection.

Detection Strategy: Focus on static signatures (stack-checking loop patterns, VEH installation, sleep call sequences) rather than behavioral analysis. YARA rules based on these patterns provide high-confidence detection.

System Impact Operations

Volume Shadow Copy Deletion

All encryption variants systematically delete Windows Volume Shadow Copies to prevent system restore:

// From enc_v2.exe and updated_enc.exe (sub_1400087d4, sub_140006bba)

// SIGNATURE STRING (exact match across variants):
"vssadmindeleteshadows/all/quietwmicshadowcopy[*] Scanning: \n"

This concatenated string reveals the command execution:

vssadmin.exe delete shadows /all /quiet
wmic.exe shadowcopy delete

Business Impact: Volume Shadow Copy deletion eliminates the Windows “Previous Versions” restore capability, forcing victims to rely on offline backups. This is a standard ransomware technique to maximize pressure on victims.

Drive Enumeration

Loop through all possible drive letters to maximize impact:

// From enc_v2.exe (sub_1400087d4)

(uint8_t)r14 = 0x41;                    // Initialize to 'A'
...
} while ((uint8_t)r15_3 <= 0x5a);       // Loop until 'Z'

Scope: ALL local drives (C:, D:, E:, etc.) regardless of drive type (HDD, SSD, USB, network-mapped drives assigned drive letters)

Debug strings indicate network share targeting capability:

"netusesrc/modules/disks.rs"  // Rust module for network enumeration

Lateral Movement Risk: A single infected endpoint can discover and encrypt network file shares accessible to the compromised user account, potentially encrypting entire department or organization file servers.

File Targeting Intelligence

The decryptor (dec.exe) reveals the encryptor’s targeting logic through its blocklists:

Folder Blocklist:

$recycle.bin, config.msi, $windows.~bt, $windows.~ws, windows,
appdata, program files, program files (x86), programdata

File Extension Blocklist:

.dll, .exe, .sys, .ini, .lnk, .msi, .drv, .cur, .hlp, .icl,
.ico, .idx, .lock, .mod, .mpa, .msc, .msp, .msstyles, .msu,
.nomedia, .ocx, .prf, .rom, .rtp, .scr, .shs, .spl, .theme,
.themepack, .url, .wpx

Executive Technical Context

What This Means: The ransomware intelligently avoids system files to maintain system operability while encrypting user data and productivity files. This ensures the victim can still use the computer to view ransom notes and attempt recovery, while all valuable business data remains encrypted.

Business Impact: Systematic targeting of all accessible storage (local drives A-Z + network shares) combined with VSS deletion creates total data loss scenario. Organizations without offline backups face complete operational shutdown.

Detection Strategy: Monitor for vssadmin.exe and wmic.exe executions with VSS deletion parameters. Alert on mass file modification operations across multiple drives. Deploy file system activity monitoring for rapid encryption pattern detection.

Variant Comparison Matrix

Technical Feature Comparison

Feature	enc_v2.exe	updated_enc.exe	enc_pervictim.exe	enc.exe	test_gui_enc_v2.exe
Reverse Engineered	FULL	FULL	FULL	Automated	Automated
Crypto Suite	RSA + ChaCha20	RSA + ChaCha20	RSA + ChaCha20	RSA + ChaCha20	RSA + ChaCha20
Custom ChaCha20	Confirmed	Confirmed	Confirmed	Unknown	Unknown
AVX Optimization	Present	Present	Runtime Dispatcher	Unknown	Unknown
CPU Dispatcher	Absent	Absent	AVX-512/AVX2/SSE	Unknown	Unknown
Per-Victim Keys	Standard	Standard	ENABLED	Unknown	Unknown
Stack Anti-Debug	Present	Present	Present	Likely	Likely
VEH Installation	Present	Present	Present	Likely	Likely
VSS Deletion	Confirmed	Confirmed	Confirmed	Likely	Likely
Drive Enumeration	A-Z Loop	A-Z Loop	A-Z Loop	Likely	Likely
Network Shares	Confirmed	Confirmed	Confirmed	Likely	Likely
Ransom Note	README.txt	README.txt	Unknown	README.txt	README.txt
Rust Artifacts	Confirmed	Confirmed	Confirmed	Likely	Likely
Compilation Language	Rust	Rust	Rust	Rust	Rust

Feature	dec.exe	dec_fast.exe	dec_pc3.exe	dec_unique.exe	test_decryptor.exe
Reverse Engineered	FULL	Automated	Automated	Automated	Automated
Password Required	–pass flag	Likely	Likely	Likely	Possibly optional
PBKDF2 KDF	Confirmed	Likely	Likely	Likely	Likely
RSA Unwrapping	Confirmed	Likely	Likely	Likely	Likely
ChaCha20-Poly1305	Confirmed (AEAD)	Likely	Likely	Likely	Likely
Blocklists	Extensive	Unknown	Unknown	Unknown	Possibly disabled
Cleanup Functions	Ransom note deletion	Unknown	Unknown	Unknown	Unknown
Stack Anti-Debug	Present	Likely	Likely	Likely	Likely
Rust Implementation	Confirmed	Likely	Likely	Likely	Likely

Development Timeline Assessment

Based on naming conventions and feature sets, the probable development evolution:

PHASE 1: Initial Development
  |-- enc.exe (basic encryptor)
  |-- dec.exe (basic decryptor)

PHASE 2: Version 2 Architecture
  |-- enc_v2.exe (enhanced with AVX optimization)
  |-- test_gui_enc_v2.exe (GUI testing variant)

PHASE 3: Targeted Enhancements
  |-- updated_enc.exe (refined enc_v2 with improved signatures)
  |-- enc_pervictim.exe (per-victim key generation, runtime CPU dispatcher)

PHASE 4: Specialized Decryptors
  |-- dec_fast.exe (performance optimization)
  |-- dec_pc3.exe (machine-specific variant)
  |-- dec_unique.exe (specialized decryption parameters)
  |-- test_decryptor.exe (QA/testing build)

Executive Technical Context

What This Means: This development timeline indicates:

Professional Software Engineering: Version control, incremental improvements, QA testing
Performance Focus: Multiple optimization passes (AVX, runtime dispatchers, “fast” variants)
Operational Flexibility: Specialized variants for different deployment scenarios
Active R&D: Not a static tool, but continuously refined malware platform

Business Impact: The extensive development investment indicates this is a strategic capability for the threat actor, not an experimental tool. Organizations should expect continued development, feature enhancements, and operational deployment.

Intelligence Assessment: The presence of testing/QA variants (test_gui_enc_v2.exe, test_decryptor.exe) demonstrates professional software development lifecycle practices with formal quality assurance processes.

Threat Actor Attribution

</table>

TTP Clustering Analysis

Comparative TTP Analysis: Comparing PoetRAT espionage tools vs enc/dec ransomware:

Technique	agent.exe (PoetRAT)	enc_v2.exe (Ransomware)	Shared
T1497 (Sandbox Evasion)	Multi-technique	Stack+Sleep+VEH	YES
T1027 (Obfuscation)	Multi-layer	Multi-layer	YES
T1547.001 (Registry Persistence)	Confirmed	Not observed	NO
T1082 (System Discovery)	Confirmed	CPU detection	YES
T1486 (Data Encryption)	Not applicable	PRIMARY	NO
T1490 (Inhibit Recovery)	Not applicable	VSS deletion	NO

Conclusion: Shared defense evasion and obfuscation techniques provide strong TTP linkage between PoetRAT espionage tools and enc/dec ransomware, supporting unified threat actor attribution.

Frequently Asked Questions

Technical Questions

Q: Why did dynamic sandbox analysis fail? A: The ransomware’s hardware-optimized ChaCha20 encryption (AVX-512) encrypts data extremely rapidly - hundreds of gigabytes in minutes. The malware encrypted the sandbox’s analysis tools themselves faster than behavioral telemetry could be collected, rendering the analysis environment inoperable. The anti-analysis techniques (stack-checking, VEH, Sleep() calls) successfully evaded sandbox detection while allowing destructive execution.

Q: How does the custom ChaCha20 implementation compare to standard libraries? A: Arsenal-237 uses completely hand-coded ChaCha20 (NOT OpenSSL, libsodium, or Windows CryptoAPI). This custom implementation features:

Professional-grade ARX (Add-Rotate-XOR) operations matching RFC 8439 specification
Multiple SIMD variants (AVX-512/AVX2/SSE) with runtime CPU dispatcher
Performance optimization exceeding standard library implementations
This level of cryptographic engineering is extremely rare and indicates professional development with specialized expertise

Q: Can the encryption be broken without the attacker’s key? A: NO. The hybrid RSA-2048 + ChaCha20 encryption is mathematically unbreakable without the threat actor’s master private key and decryption password. Cryptanalysis would require billions of years of supercomputer time. Reverse engineering identified no implementation weaknesses - the cryptography is equivalent to banking/government-grade standards. Offline backup restoration is the ONLY viable recovery method.

Q: What makes the per-victim key generation significant? A: The enc_pervictim.exe variant generates unique encryption keys for each victim organization (not a single master key for all campaigns). This indicates:

Deliberate targeting (not opportunistic spray-and-pray)
Operational security (single key compromise doesn’t affect other victims)
Price discrimination capability (ransom based on victim organization wealth)
Sophisticated operational methodology (reconnaissance -> targeting -> customized deployment)

Business Questions

Q: Should we pay the ransom to decrypt our files? A: NOT RECOMMENDED. Rationale:

Industry data: 35% of ransom-paying organizations do NOT receive functional decryption tools
Payment funds advanced threat operations
Payment encourages future targeting
Without confirmed attribution, payment may create legal exposure if threat actor falls under sanctions regimes
Offline backup restoration is the only cryptographically-independent recovery method

Q: What are the compliance implications of an Arsenal-237 ransomware incident? A: Significant regulatory obligations:

GDPR (EU): 72-hour breach notification if customer data encrypted, potential fines up to 4% global annual revenue
HIPAA (Healthcare): 60-day notification requirement if PHI encrypted, potential fines up to $1.5M per violation category
PCI DSS (Card Processing): 72-hour incident reporting to card brands, mandatory forensic investigation
SOX (Publicly Traded): 8-K filing with SEC if material impact, internal controls assessment
State Breach Laws: Multi-state notification requirements, attorney general notification

Q: How can we detect Arsenal-237 ransomware if it evades automated sandboxes? A: Detection requires multi-layered approach:

Static Signatures: Deploy YARA rules for ChaCha20 constant (“expand 32-byte k”), VSS deletion signature
Behavioral EDR: Real-time monitoring for mass file modification patterns (not time-limited sandbox analysis)
Network Controls: Block infrastructure 109.230.231.37 at perimeter
Threat Hunting: Proactive search for Rust ransomware artifacts, PoetRAT espionage tools (agent.exe, steal_browser.exe)
VSS Monitoring: Alert on vssadmin.exe and wmic.exe with deletion parameters (high-fidelity indicator)

Q: What is the estimated recovery timeline for an Arsenal-237 ransomware incident? A: For REBUILD and RESTORE approach:

Hours 0-4 (Emergency): Network isolation, infrastructure blocking, backup securing, threat hunting deployment
Hours 4-24 (Containment): Complete threat hunt, forensic acquisition, eradication planning, stakeholder communication
Days 2-3 (Eradication): Malware removal, PoetRAT persistence elimination, system rebuilds, credential rotation
Days 3-7 (Recovery): Data restoration from backups, integrity validation, phased return to operations
Week 2+ (Post-Incident): Lessons learned, security improvements, compliance activities, threat intelligence sharing
Total Environment Recovery: 5-7 days (depending on organization size and backup infrastructure)

BLUF (Bottom Line Up Front)

Executive Summary

Business Impact Summary

Key Risk Factors

Recommended Actions

Table of Contents

Quick Reference

File Identification

Encryption Variants (5 Total)

Decryption Variants (5 Total)

Discovery Context

Executive Technical Summary

Business Context

Key Business Impacts

Detection Challenges

Executive Risk Assessment

Deep Technical Analysis

Execution Flow Overview

Encryption Workflow (enc_v2.exe Reference Model)

Decryption Workflow (dec.exe Reference Model)

Executive Technical Context

Cryptographic Architecture

Hybrid Encryption Workflow

Encryption Process

Cryptographic Strength Assessment

Executive Technical Context

Custom ChaCha20 Implementation

ChaCha20 Identification Evidence

ARX (Add-Rotate-XOR) Core Operations

Runtime Hardware Optimization (enc_pervictim.exe)

Executive Technical Context

Anti-Analysis Techniques

Signature 1: Stack-Based Anti-Debugging Loop

Signature 2: Vectored Exception Handling (VEH)

Signature 3: Obfuscated Execution Flow

Signature 4: Unhandled Exception Filter

Comparative Analysis

Executive Technical Context

System Impact Operations

Volume Shadow Copy Deletion

Drive Enumeration

Network Share Discovery

File Targeting Intelligence

Executive Technical Context

Variant Comparison Matrix

Technical Feature Comparison

Development Timeline Assessment

Executive Technical Context

Threat Actor Attribution

TTP Clustering Analysis

Frequently Asked Questions

Technical Questions

Business Questions

IOCs

Detections

License