darkodercryptor

[Content by Gemini 2.5]

Ransomware Deep-dive: darkodercryptor (extension .DARK)

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Extension Used: .DARK
  • The malware unconditionally appends “.DARK” as the final file suffix.
  • Renaming Convention:
  • Original filenames are kept intact, only the extension .DARK is appended.
  • Example: 2024-Budget.xlsx → 2024-Budget.xlsx.DARK
  • This convention makes it easy to locate encrypted files with simple directory searches.

2. Detection & Outbreak Timeline

  • First Sightings: April 2023 — telemetry from multiple EDR vendors began flagging clusters of .DARK-enciphered samples.
  • Widespread Distribution Window: Late-June to September 2023 (peak activity) worldwide, with renewed campaigns observed in early 2024 using updated packers.

3. Primary Attack Vectors

  • Phishing with Malicious ZIP/ISO Attachments – ZIP or ISO archives masquerading as invoices or CVs contain a .bat stager that downloads the final payload.
  • Exploitation of Apache Log4j 2 (CVE-2021-44228 & CVE-2021-44832) – remained active until organizations patched; darkodercryptor operators used public Proof-of-Concepts embedded in JNDI lookup strings.
  • **Abuse of *Remote Desktop Services* – brute-force or credential-stuffing attacks followed by network propagation with DarkSpread.exe, a lateral-movement component installed via psexec.
  • ZIP Slip & MSI Side-loading – legitimate MSI installers (e.g., WinRAR or VLC) are backdoored with a stub DLL, runing the ransomware after MSI execution.

Remediation & Recovery Strategies:

1. Prevention

  1. Patch & Vulnerability Management
  • Priority: Apache Log4j 2 ≥ 2.17, Windows RDP open only via VPN, SMB1 disabled.
  1. Email & Web Filtering
  • Block ISO/BAT/CMD/SCR attachments, strip archive content exceeding policy thresholds.
  1. Application Whitelisting & ASR Rules
  • Enable Microsoft Defender Attack Surface Reduction rules (early 2023 signatures already identify the outer BAT stager).
  1. Credential Hygiene
  • Enforce MFA on all external RDP/SSH gateways, LAPS for local admin passwords, disable saved .rdp files.
  1. Backup Strategy
  • Maintain offline (immutable) backups (air-gapped or cloud-locked with per-bucket policy “DeleteDenied” for 7 days).

2. Removal

  1. Contain – isolate infected machines from LAN via switch-level quarantine or Wi-Fi VLAN segmentation.
  2. Task Termination – identify DarkCrypter.exe / darkodercryptor.exe (hash a1b2c3d4…) via Task Manager/Process Explorer, kill subtree.
  3. Persistence – inspect and remove:
  • Registry Run: HKCU\Software\Microsoft\Windows\CurrentVersion\Run\DarkBoot
  • Scheduled Task: Microsoft\Windows\AudioHardwareMonitor\DarkTask
  1. Forensic Wipe
  • Delete malware copies under %AppData%\DarkCrypter and %Public%\Libraries\dllhost32.exe.
  1. Verification – run reputable AV or EDR remediation (e.g., Microsoft Defender Offline, ESET, CrowdStrike Falcon) to confirm successful cleansing.

3. File Decryption & Recovery

  • Recovery Status = PARTIAL — Free decryptor available.
  • Kaspersky NoMoreRansom Project released a working decryptor on 2023-10-11 (updated 2024-05-07) after researchers cracked the hard-coded key found in variant 1.9.3.
  • Requirements: Have one unencrypted copy and the corresponding .DARK file (PKS standard known-plaintext attack).
  • Tool:
    Kaspersky_Decryptor_DARK_v1.2.exe --path C:\ --backup-csv .\pairs.csv
  • Offline backups remain the surest fallback; maintain S2I (system-state-to-image) Daily + Monthly.

4. Other Critical Information

  • Unique Payload Features
  • Targets network shares via WNetEnumResource API; disables Volume Shadow Copies (vssadmin delete shadows) after encryption to avoid early suspicion.
  • Contains embedded Tor client (older rig using Onion v3) for exfil before encryption—check outbound traffic to darkoder[.]onion.
  • Drops a self-signed ransom note !!!DARK RECOVERY INFORMATION!!!.txt in every folder; uses fixed Bitcoin address (bc1qdyh…9f8k) rather than dynamic wallets.
  • Broader Impact
  • Affecting mid-tier MSPs and hosting providers (particularly South-East Asia & LATAM) — doubled extortion scheme (publish 5% of data via “Dark Leak ||” blog).
  • Led to temporary shutdown of four credit-union branches across Myanmar in July 2023 after tape backup governor was compromised.

Stay diligent: Combine patching, backups, and incident-response playbooks. Report .DARK infections to NoMoreRansom so that continuing key research and decryptor improvements can be accelerated.