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

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

Recommended Actions

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

Quick Reference

Detections & IOCs:

• enc/dec Ransomware Detection Rules
• enc/dec Ransomware 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

The methodical execution flow shows professional software engineering with a clear separation of concerns across anti-analysis initialization, obfuscated dispatch, cryptographic operations and system impact functions. Pairing encryption with VSS deletion gives the attacker defense in depth, so the data stays inaccessible even where one recovery method survives.

The systematic approach maximizes operational damage while leaving as few detection opportunities as possible. The result is complete data loss with no viable recovery path except offline backups.

The high-confidence detection points are the initialization phase, meaning the stack-checking loops, and the system impact operations, meaning the VSS deletion commands. The cryptographic operations on their own give little to detect on, because the implementation is custom.

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

The hybrid cryptographic architecture pairs the mathematical strength of RSA-2048 for key protection with the performance of ChaCha20 for file encryption. That design pattern is identical to the one behind industry-standard secure communications protocols such as TLS and Signal.

Without the operator’s master RSA-2048 private key and the decryption password, file recovery is mathematically impossible, and paying is no guarantee of a working decryptor either. Offline backup restoration is the only cryptographically independent recovery method.

The custom ChaCha20 implementation is not library-based, which defeats signature-based monitoring of cryptographic APIs. Detection has to rest on file system behavior, meaning mass encryption operations, rather than on cryptographic function calls.

Custom ChaCha20 Implementation

The ChaCha20 implementation is not built on any standard cryptographic library, not OpenSSL, not libsodium, not the Windows CryptoAPI. It is completely custom, hand-coded, and engineered for performance at a professional level.

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.

The assembly pattern of Add-Rotate-XOR operations is unique to the ChaCha20 quarter-round function. That exact sequence does not appear in AES, Salsa20 or any other cipher, which makes it 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:

1. Check for AVX-512 instruction set support
2. Check for AVX2 instruction set support
3. 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

SIMD optimization works like a factory assembly line. Rather than encrypting files one at a time, the malware processes several in parallel. Performance engineering at that level takes:

• 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

Hardware-optimized encryption lets an attacker take an entire enterprise file server in minutes rather than hours, which collapses the detection and response window. The safe assumption after an initial compromise is rapid, network-wide encryption.

This is not the work of commodity ransomware developers. It points to a professional development team with specialized cryptographic engineering capability.

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

Executive Technical Context

These shared signatures give high-confidence attribution to a single actor and make solid YARA rules possible. Their consistency across variants points to systematic engineering practice and deliberate code reuse.

Multi-layer anti-analysis defeats automated sandbox analysis and makes reverse engineering considerably harder, so a standard analysis platform will not produce behavioral detection here.

The signatures worth building on are static ones, meaning the stack-checking loop patterns, the VEH installation and the sleep call sequences, rather than behavior. YARA rules over those patterns detect with high confidence.

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

Deleting the Volume Shadow Copies removes the Windows Previous Versions restore capability and pushes the victim onto offline backups. It is a standard ransomware move for maximizing pressure.

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'

The sweep covers every local drive (C:, D:, E: and onward) whatever the type, taking in HDDs, SSDs, USB media and network-mapped drives that hold a drive letter.

Network Share Discovery

Debug strings indicate network share targeting capability:

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

A single infected endpoint can find and encrypt every network file share the compromised account can reach, which can take out an entire department’s or an entire organization’s 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

The ransomware deliberately avoids system files so the machine keeps working while the user data and productivity files go under. The victim can still boot the computer, read the ransom note and attempt recovery, with every piece of valuable data encrypted.

Sweeping all accessible storage, local drives A to Z plus network shares, and then deleting the shadow copies produces total data loss. Without an offline backup that is a complete operational shutdown.

To detect it, watch for vssadmin.exe and wmic.exe running with VSS deletion parameters, alert on mass file modification across several drives at once, and keep file system activity monitoring in place to catch the encryption pattern early.

Variant Comparison Matrix

Technical Feature Comparison

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

That development timeline shows:

• 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

That much sustained development marks this as a strategic capability for the actor rather than an experiment, so continued development, new features and further operational deployment should all be expected.

Testing and QA variants sitting in the same directory, test_gui_enc_v2.exe and test_decryptor.exe, point to a professional software development lifecycle with formal quality assurance behind it.

Threat Actor Attribution

</table>

TTP Clustering Analysis

Setting the PoetRAT espionage tools against the enc/dec ransomware gives:

The shared defense evasion and obfuscation techniques give strong TTP linkage between the PoetRAT espionage tools and the enc/dec ransomware, which supports attributing both to one actor.

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: Does an incident like this carry regulatory consequences? A: Very likely, and which ones depends entirely on the jurisdiction and the data involved. That question belongs with counsel rather than with a threat report. What the technical evidence establishes, and what such an assessment turns on, is that encryption here is preceded by data access, so an incident is not confined to availability.

• 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)

IOCs

• enc/dec Ransomware IOCs

Detections

• enc/dec Ransomware Detection Rules

License

© 2026 Joseph. All rights reserved. Free to read, but reuse requires written permission.