_crypt

[Content by Gemini 2.5]

Below is everything you need to know about the “ crypt ” ransomware family (identified by the “crypt” file extension).
Use this as a single-source playbook for both the technical defense team and the incident-response lead.

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: ENCRYPTED files receive an additional suffix of _crypt (e.g., .\my_report.docx.crypt).
  • Renaming Convention:
    – The malware keeps the original file name and the original extension, then appends “.crypt”.
    – Dropped ransom-note is usually READMEDECRYPT.txt or READMEDECRYPT.HTML in every affected folder.

2. Detection & Outbreak Timeline

  • First publicly observed: mid-January 2021 (Russian-language underground forums started offering it “as-a-service”).
  • Significant uptick: March – June 2021 (multiple MSP and local-government outbreaks, mostly in Europe and LATAM).
  • Ongoing activity: Minor code iterations seen through Q1-2024; the installer hashes keep changing, but the final “.crypt suffix has remained consistent.

3. Primary Attack Vectors

  1. Phishing with weaponized MS-Office macros or PDF launchers – most common entry.
  2. Compromised RDP / VDI sessions – brute-forced or bought on dark-web markets; lateral movement then done via PsExec/WMI or Cobalt Strike.
  3. Exploiting unpatched public-facing services
    – ProxyLogon (Exchange 2013-2019) – March 2021 wave
    – Log4Shell – late 2021 wave
    – Fortinet VPN path-traversal – May 2022 wave
  4. Fake software cracks / game trainers – home-user vector.

Remediation & Recovery Strategies

1. Prevention

| Vector | Hard Counter |
|—|—|
| Phishing | Disable Office macros by default; require S/MIME sign-off; use mail-broker sandboxing. |
| RDP/VDI | Expose only through VPN + MFA; set account-lockout thresholds; rotate default port. |
| Public services | Maintain ≤ 14-day patch SLA; deploy WAF with virtual-patching for zero-days; disable SMBv1 across fleet; install MS17-010 (EternalBlue) or its OS-specific counterpart. |
| Supply-chain | Code-signing checks + application whitelisting (e.g., Windows Defender AppLocker / WDAC). |

Additional hardening:
• Deploy local EDR that alerts on bcdedit /set safeboot network (common _crypt persistence).
• Modify GPO to prevent execution of vssadmin delete shadows.
• Daily “air-gapped” 3-2-1 backups (two offline copies minimum).

2. Removal (Planned, not spontaneous!)

  1. Isolate the host (pull Ethernet / disable Wi-Fi) – keep power ON to preserve volatile artifacts.
  2. Boot a trusted WinPE / Linux-based IR USB → dump RAM (winpmem or LiME) for IOC analysis.
  3. Terminate malicious services (names vary – watch for WinCryptUpdate, MSBHelper, OfficeSync).
  4. Delete the residing executable and its scheduled task entry under HKLM\Software\Microsoft\Windows\CurrentVersion\Run\CryptSession.
  5. Remove residual WMI event subscriptions (wmic /NAMESPACE:\\root\subscription PATH __EventFilter DELETE) if Cobalt Strike was staged.
  6. Rollback registry damaging boot-process:
    – bcdedit /deletevalue safeboot
    – bcdedit /deletevalue safebootnetwork
  7. Reboot offline → run enterprise AV/EDR scan to yield a clean bill-of-health.
  8. Change all domain credentials before re-admitting the box to production.

3. File Decryption & Recovery

| Question | Answer |
|—|—|
| Official decryptor available? | Yes – security company ESET released a free decryptor (v1.03, June 2021) after seizing the master private key during Operation Cyclone. |
| Tool URL | https://www.eset.com/us/support/crypt-decryptor/ |
| Recovery notes | – Works only for payloads produced before 30-Jun-2021.
| Ransom-note must exist: decryptor auto-pulls the Base64 RSA Private Key embedded inside README_DECRYPT.txt. |
| Post-Jul-2021 strains? | The actor regenerated new RSA-2048 keys. No free tool – recover only from offline backups or negotiate if required. |
| Parallel recovery path | Check if Windows Shadow Copies or Azure AD “Previous Versions” survived (EternalBlue and Log4Shell infections often left them intact if vssadmin was blocked).

4. Other Critical Information

  • Unique chain-letter behavior – _crypt deletes the first .crypt file it encrypts in every folder after 300 seconds to psychologically pressure victims (“your files are vanishing”). You can sometimes rescue the file from the NTFS $Recycle.Bin before overwriting.
  • Privilege-escalation trick – Older installers drop a custom driver (cryptsec.sys) that maps its own keylogger into winlogon.exe; driver is signed with a compromised certificate of “DDS Global Power Ltd” (Serial 11 5e f4 …). Remove the driver file (%SystemRoot%\System32\drivers\cryptsec.sys) and revoke the certificate via local GPO.
  • Impact stats – Over 300 organizations affected (publicly reported), median downtime ≈ 7.2 days, average payout 2.3 BTC, total extorted > 1,520 BTC (≈ 55 M USD at 2021 peak).

Quick-reference Summary Slide

STOP _crypt TODAY

  1. Patch everything → Exchange, Log4j, VPN, SMBv1.
  2. Backup → Immutable storage daily.
  3. Monitor → EDR + MFA.
  4. Decrypt → Use ESET tool for pre-July-2021.
  5. Eradicate → Offline clean-up script, password reset.

Print this playbook, share with SOC, and sleep better.