cry36

[Content by Gemini 2.5]

Technical Breakdown: Cry36 Ransomware (ran by the BTCWare family)

  1. File Extension & Renaming Patterns
    • Confirmation of File Extension: ‑.cry36
    • Renaming Convention:
    Original name  ➜  [filename].[original-ext].id-[victim-machine-id].[attacker-mail1&2].cry36
    (typical example: Invoices.xlsx → Invoices.xlsx.id-A1B2C3D4.[[email protected]].cry36)

  2. Detection & Outbreak Timeline
    • First publicly surfaced: March 2017 as a new variant of the BTCWare family.
    • Peak activity waves: April–August 2017, with smaller flare-ups into 2018; continues to appear in incident-response cases when legacy servers remain unpatched.

  3. Primary Attack Vectors
    • Propagation Mechanisms:
    – RDP brute-force or credential stuffing to gain admin-level access.
    – Manual deployment by attackers via Cobalt Strike / PSExec once they land on the network.
    – Exploits for CVE-2017-0144 (EternalBlue SMBv1) and CVE-2017-0145 (DoublePulsar backdoor) still seen in perimeter scans.
    – Phishing e-mails with booby-trapped .zip → .js/.wsf in less-common infection chains.

Remediation & Recovery Strategies

  1. Prevention (Proactive Measures)
    • Disable/uninstall SMBv1 across Windows fleet; apply MS17-010.
    • Restrict RDP: expose only behind VPN or RD Gateway, enforce 2FA, account lockout after five failures.
    • Remove local admin for day-to-day users, disable RDP shadowing, use LAPS for randomized local admin passwords.
    • Implement network segmentation: separate iSCSI / backup VLANs, deny SMB from client endpoints to domain controllers.
    • Continuous, offline (immutable) backups: 3-2-1 rule plus daily Veeam or Bacula jobs to tape or object-lock cloud storage.
    • Application whitelisting (AppLocker, WDAC).
    • Patch cycle: ≤ 14 days for OS and third-party browser / mail clients to curb any email chains that piggy-back exploit kits.

  2. Removal (Infection Cleanup)
    Isolate:

  3. Disconnect LAN/Wi-Fi immediately; leave Wi-Fi off until fully remediated.

  4. Identify last elevated user; verify no lateral movement in logs.

    Secure forensic snapshot:

  5. Take memory dump (winpmem) and full-disk .vmdk/.raw if legal/insurance requires—preserve Bitcoin wallet note.

  6. Offline Kaspersky Rescue Disk or Bitdefender LiveCD boot; run AV engine signature Ransom.BTCWare.XX.

  7. Search persistence:
    – Registry Run keys (HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run) for random-name executables.
    – Scheduled tasks carrying a base-64 PowerShell command.
    – WMI subscriptions left by Cobalt Strike.

  8. Remove infection binaries and drop any additional tools (Mimikatz, Cobalt beacon).

  9. Patch and re-secure RDP: freeze account, rotate domain admin, roll Kerberos krbtgt 2×.

  10. File Decryption & Recovery
    • Recovery feasibility: Free decryptor exists.
    • Tools/method:
    – Emsisoft Decryptor for Cry36/BTCware v3.2 (current) ­– works for most UID-A1B2C3D4 versions with 1024-bit RSA key that the attacker reused.
    – Check first with btcware.exe –check inside the decryptor; if “key not found,” move to backups.
    • Manual AES-256 + RSA-1024 key reconstruction is infeasible without operators’ private key; pay-ransom angle is discouraged and unreliable (keys often purged after two-week window).
    • Post-decryption: run CHKDSK /F and fsck to repair metadata corruption if volumes were damaged.

  11. Other Critical Information
    • Ransom note dropped as #_README_#.inf or #_DECRYPT_#.txt; identical text across subvariants (“All your files have been encrypted… send 0.5–0.8 BTC”).
    • Stops/home/termination lists include critical Windows services (WinDefend, MBAMService) to avoid self-reversal.
    • Older BTCWare siblings: .cry, .aleta, .nuclear, .wallet—decryptor partly overlaps for old keys (> May 2017 dumped by C2 leak).
    • Unique characteristic: leverages legitimate closed-source encryption; but once operator cleanup happened (2018 opsec slip-up) their master private keys appeared on VirusTotal, enabling universal decryption for extant samples marked with @@[email protected], @@[email protected], and @@[email protected].

Broader Impact
Cemented the playbook for hands-on-keyboard ransomware: initial foothold via RDP rather than worm-only spread, emphasizing the need for MFA and jump-host architecture. Cry36 and its BTCWare cousins drove MSPs and insurers to treat Windows Server systems older than 2012 as “crypto mice”—actionable pressure that still speeds SMB patching budgets today.