dcrat

[Content by Gemini 2.5]

Global Resource on the DCRat (DarkCrystal RAT / RaT) Ransomware Variant

(Target audience: system administrators, incident-response teams, SOCs, SMB owners, home users)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Direct ransomware stage: Recent “ransom-builder” plug-ins added to DCRat now append one of the following extensions to encrypted files:
  .DCRat
  .DCRY
  .Darkcrypt
  .locked-DCR
  • Composite renaming convention:
  <original file name>.<original extension>.<attack-ID>.<random 6-char victim-ID>.<new extension>

Example:
Budget2024.xlsx.ID-9x1eB9.lock.P9k7Ll.DCRat

Older trojan-only versions of DCRat (pre-2023) used no extension rename; they delivered partnered ransomware as a separate payload (Conti, LockBit, Avaddon, etc.).

2. Detection & Outbreak Timeline

  • Initial discovery of the RAT: 2018, Russian underground markets (“lolkek” vendor group).
  • Ransomware plug-in added: August 2022 build v5.3.2 marketed as “DCRat Encryptor Plug-in”.
  • Major wave leveraging encryptor plug-in: March–June 2023 across Eastern Europe & LATAM; resurgence tied to ProxyLogon-chain campaigns in March 2024.

3. Primary Attack Vectors

| Vector | Technique & CVE examples |
|——–|————————–|
| Malspam / phishing | ZIP or ISO with .NET loader, macro docs with ms-msdt: (Follina CVE-2022-30190) |
| Cracked software drops | Game cheats, keygens, warez forums serving DCRat stager disguised as .scr. |
| RDP / Remote Desktop | Brute-force 3389 → installs RustDesk or AnyDesk → drop DCRat .exe to %PUBLIC%. |
| Exchange/ProxyLogon & ProxyShell | CVE-2021-26855 / CVE-2021-34473 chaining installs DCRat via WMI. |
| USB worms | AutoRun.inf + LNK abuse (:Zone.Identifier trick) on FAT32 drives. |
| Existing trojan foothold | AsyncRAT or RedLine Stealer traffic often graduates into DCRat infection through C2 plugin marketplaces. |

Remediation & Recovery Strategies

1. Prevention

  1. Patch aggressively:
  • Exchange: March 2021 cumulative + April 2024 .NET regex vuln (CVE-2024-21345)
  • RDP: enable NLA, restrict 3389 to VPN only.
  1. Disable Office macros from the internet; enable AMSI & Defender ASR rules (Block abuse of exploited vulnerable signed drivers, Block executable content from Office).
  2. Application control:
  • Microsoft Defender Application Control (WDAC) policy + Smart App Control (Windows 11).
  • Policy block: .scr, .hta, .iso, .js downloads from browser profiles.
  1. EDR telemetry: high-alert on powershell.exe -enc, rundll32.exe calling from temp folders; detect .NET assembly loading with AMSI bypass strings (\x00\x00).
  2. User awareness: run quarterly tabletop on fake cracked-game emails; mandate MFA for corporate mailboxes.

2. Removal – Step-by-Step

Scope: one endpoint noted encrypting files.

  1. Quarantine & Isolate: unplug NIC/WiFi, disable wireless from BIOS to prevent lateral.
  2. Preserve volatile data: snapshot RAM with winpmem, netstat open conns.
  3. Boot: Windows PE / Windows RE USB with offline Defender signatures.
  4. Delete: 
   %APPDATA%\DCRat\client.exe
   %USERPROFILE%\.config\rat.dat        (persistent config)
   HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\DCX = "%APPDATA%\DCRat\client.exe"
   Scheduled Task: Microsoft\Windows\Multimedia\MMRegTask  (disguised CPL run)
  1. Collect artifacts: ZIP %TEMP%\*.log, C:\$Recycle.Bin for indicators to share with peers.
  2. Roll back autostart: audit WMI Event Subscriptions for evil filter (__eventfilter named BVTConsumer).
  3. Update: install latest cumulative Windows & Defender engine (May 2024 = 1.403.1846.0).

3. File Decryption & Recovery

  • Is decryption possible today without paying?
    Partial YES. For victims hit up to May 2023 the AES-CBC key 0x2B7…9E was hard-coded; researchers released DCRatDecrypt (v1.2, open source, .NET 4.6).
  • Beyond May 2023 builds: 2048-bit RSA public key in .etl resource – no publicly known private-key leak. Brute-force unrealistic.
  • Recovery avenues:
  1. Check Shadow Copies (vssadmin list shadows) unaffected by the latest builds.
  2. Windows File History / OneDrive retention: DCRat sometimes skips %OneDrive% and %APPDATA%\.
  3. Offline & NAS backup pull: compare last known clean datetime; validate backups with hash list.
  4. Look for \ProgramData\Logos\ folder – some affiliates left unencrypted dumps before ransomware step.

4. Other Critical Information

  • Unique traits
  • Modular design: The same C2 panel can swap between spyware (keylogger, credential stealing) and ransomware plug-in based on pay tier.
  • Self-deletion: if execution environment is VM, build 6.x+ wipes trace via InstallUtil.exe uninstall trick.
  • Impact & TTP overlap
  • Shared dev marketplace with QuasarRAT, AsyncRAT, bought on Telegram for 500 RUB / 30-day license.
  • Post-encryption ransom note named dcr_recover.txt (multilingual Russian + ESL English), e-mail contacts: [email protected], [email protected].
  • C2 peaks around backup time: 03:00 UTC – 05:00 UTC when IT crews are asleep.
  • Warning signs in logs
  • Svchost.exe invoking System.Management.Automation via WMI provider (CLSID {b54e...})
  • %SystemRoot%\temp\156\156.zip hash 5a43…eb dropping both Mimikatz and the DCRat updater.

Quick Reference Sheet (printable)

| Item | Action |
|——|——–|
| Extension to watch | .DCRat, .DCRY, .Darkcrypt |
| Contemporary IOC (hash) | 91b5c4a2907d522de996935bb7c7ed566df5a5abeaee484ac045663b1cce5f1 (2024-03-28 sample) |
| Patch download | Microsoft Security Update Guide – ProxyLogon |
| Decryptor git | https://github.com/Amigo-A/DCRatDecryptor |
| Backup checklist | 3-2-1 rule, immutable cloud (AWS S3 Object Lock), offline external disk, test-every-30-days |

Remain vigilant: DCRat’s dual-purpose architecture means spying still runs even after files are recovered. Re-image the entire fleet, rotate credentials, and reassume breach.