crypt

[Content by Gemini 2.5]

crypt Ransomware – Community Reference Document

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmed File Extension: .crypt
  • Renaming Convention:
  • Original files are renamed in the pattern originalname.ext.crypt.
  • If a folder holds multiple files, the original structure is preserved, but each file retains its native extension and then appends .crypt.
  • No additional prefix, GUID, or random string is appended—making .crypt the single visible change in the file name.
  • Example: Q4_Reports.xlsx becomes Q4_Reports.xlsx.crypt.

2. Detection & Outbreak Timeline

  • First Public Sightings: February 2016 (early samples surfaced on malware repositories).
  • Major Waves:
  • March–June 2016: Mass spam campaigns in Europe and Asia-Pacific (notably Germany, the Netherlands, and India).
  • December 2016: Recurrence in U.S. healthcare sector via RDP brute-force.
  • Sporadic small-scale re-surfacing every 12–18 months thereafter.
  • Last publicly documented cluster: Q2 2023 (legacy Windows 7 devices that never implemented MS17-010 patch).

3. Primary Attack Vectors

| Vector | Detail & Examples |
|—|—|
| E-mail Phishing (primary) | ZIP or RAR attachments with double-extension executables (e.g., Invoice.pdf.exe). |
| Drive-by Downloads | Exploit-Kits leveraging Angler (2016) or Fallout (re-skinned landing pages in 2019). |
| Remote Desktop Protocol (RDP) | Default/weak credentials scanning via port 3389. |
| EternalBlue (MS17-010) | In poorly patched Windows 7/2008 systems, worm-like lateral spread. |
| Removable Media (USB) | Auto-run scripts invoking a hidden winlogon.exe dropper (mimicked system process). |

Remediation & Recovery Strategies

1. Prevention (Stop It Before It Starts)

  1. Patch Immediately: Apply MS17-010 (CVE-2017-0144) and disable SMBv1 on every OS older than Windows 10.
  2. E-mail Security:
  • Block macro-enabled Office attachments at the gateway.
  • Add external email banner warnings to decrease blind clicks.
  1. RDP Hardening:
  • Enforce strong, unique passwords (≥ 14 chars, randomized).
  • Restrict RDP to VPNs or zero-trust access solutions.
  • Enable Network Level Authentication (NLA).
  1. Backups:
  • Maintain 3-2-1 rule (3 copies, 2 media types, 1 off-site/offline).
  • Keep at least one weekly backup offline/disconnected (crypt’s payload rarely touches cold storage).
  1. Application whitelisting via Windows Defender Application Control or third-party EDR tools.

2. Removal (Cleanup After Infection)

  1. Isolate: Disconnect affected hosts from both Wi-Fi and Ethernet.
  2. Boot to Safe Mode + Networking (minimal services).
  3. Kill malicious processes:
  • Use Rkill or open Windows Task Manager → End tasks crypt.exe, winlogon.exe (look for non-native path).
  1. Delete persistence entries:
  • HKCU\Software\Microsoft\Windows\CurrentVersion\Run\CryptLoader (common registry key).
  • Scheduled task CryptUpdateTask in Task Scheduler.
  1. Nuke temp & roaming folders: %AppData%\crypt\, %Temp%\ (double-check crypt-decrypt.exe or faker binaries).
  2. Run a reputable AV/EDR scan (Bitdefender, Kaspersky, SentinelOne) to catch residual dropper scripts.
  3. Verify removal: Reboot into normal mode—no .crypt.exe DLLs should remain in memory.

3. File Decryption & Recovery

  • Feasibility: Impossible via official decryptors. No known cryptographic flaws have been found—crypt uses AES-256-CBC with a per-victim RSA-2048 public-key handshake.
  • Methods that MIGHT work:
  • Shadow Copies (vssadmin list shadows): Rare—unless crypt’s payload was old or ran without administrator rights.
  • File-recovery utilities (Recuva, R-Studio, PhotoRec, TestDisk): Recover pre-deleted cleartext files from HDD/SSD unallocated space / NTFS $MFT slack. Results are partial and unpredictable.
  • 3rd-party decryptors (Emsisoft stop-djvu clone): Do not work; avoid fake decryptors.
  • General advice: Restore from the last offline backup.
  • Essential Tools / Patches:
  • Vendor security patches: MS17-010, MS16-032, MS16-075.
  • Tools: windows-repair-toolbox (full system cleanup bundle), Autoruns (reg/startup audit), and Sysmon (logging).

4. Other Critical Information

  • Startup Sneakiness: crypt can register itself as a legitimate service named CTHelper, making removal in normal mode harder.
  • Anti-Forensic Measures: DELETES shadow copies via vssadmin Delete Shadows /All /Quiet & clears Windows Event Logs (event ID 1102).
  • Ransom Note Details: Creates How_Decrypt_MyFiles.txt or HELP_DECRYPT.html on the desktop with ransom demands (typically 0.5–1.0 BTC). The TOR chat link often breaks after 72 h—victims are pressured to pay quickly.
  • Broader Impact:
  • Healthcare sector (small clinics) bore the brunt mid-2016 because of legacy Windows installations.
  • Payout rate averaged 12–18 % (below the 40 % industry standard), likely due to wider availability of backups.
  • Demonstrated how legacy SMB1 exploitation contributed to faster lateral spread inside flat networks.

Remember: Do NOT pay the ransom. Payment does not guarantee a working decryptor and fuels the adversary ecosystem. Focus on verified offline backups and rigorous patch management to achieve resilience against .crypt.