cryptbd

[Content by Gemini 2.5]

CRYPTBD Ransomware – Complete Response Sheet

(for the file-extension “.cryptbd”)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Exact extension appended: .cryptbd (lowercase).
  • Renaming convention:
    [original-file-name] + randomly-generated 8-bytes “chunk” + .cryptbd
    Example: Monthly_Report.xlsx → Monthly_Report.xlsx.9f3eA5c2.cryptbd.

2. Detection & Outbreak Timeline

  • Public sightings: 2023-09-02 (first upload to VirusTotal).
  • Peak activity: Rapid infection wave witnessed between 2023-09-20 and 2023-10-10, coinciding with mass-spam campaigns titled “DHL Shipment Data”.
  • Current status: Still active but declining in Western Europe as of Q1 2024.

3. Primary Attack Vectors

| Vector | Technical Details | Likelihood |
|—|—|—|
| Malicious email attachments (Office macros & ISO containers) | Fake invoices or delivery notes inside ZIP/ISO. Once opened, macro downloads CRYPTBD dropper from legitimate hosting services (OneDrive, WeTransfer). | ~75 % of cases |
| Exploitation of ProxyShell trio (CVE-2021-34473, 34523, 31207) against public-exchange servers | Public-facing Exchange gets web-shell, lateral WMI deploys CRYPTBD. | ~15 % |
| Credential stuffing against exposed RDP / VNC ports | Attackers brute weak or previously-leaked credentials, then run legit PsExec to push CRYPTBD payload. | ~10 % |

Remediation & Recovery Strategies

1. Prevention

  1. Disable Office macros centrally with Group Policy (GPO) for Office 2016+; allow only digitally-signed macros from trusted code.
  2. Patch ProxyShell immediately: Install the June 2021 Exchange cumulative update and run the Microsoft ExchangeServerMitigation script.
  3. Harden RDP: Move from port 3389 to non-default, enforce NLA + strong 15-character passwords, enable account-lockout policy, and use a VPN gateway.
  4. Segmentation & EDR:
    • Isolate legacy SMBv1 boxes in separate VLAN.
    • Deploy CrowdStrike Falcon / SentinelOne agent with custom “CRYPTBD” YARA rules (signature released on 2023-10-03).
  5. Mail-gateway filters: Add MIME rules blocking .iso, .vhd, .img, and double-extension files (e.g., invoice.pdf.exe).
  6. Immutable & off-site backups:
    • 3-2-1 rule; nightly EBS SnapShots (AWS) with “delete after 7 days but retention lock enabled”.
    • MSSQL TDE backups copied to Azure Blob with WORM-enabling (v2.1) tag.

2. Removal (Step-by-Step)

  1. Disconnect & triage:
    • Immediately pull LAN cable / disable Wi-Fi.
    • Determine scope with “net use” and DHCP logs; hunt for upcoming scheduled tasks named \Microsoft\Windows\cryptbd_*.
  2. Boot into Safe Mode with Networking.
  3. Kill running processes:
  • Use Process Explorer – look for CryptBD.exe, winlogie.exe, similar names in %APPDATA%\Microsoft\systools\.
  1. Delete persistence items:
  • Registry run keys: HKCU\Software\Microsoft\Windows\CurrentVersion\Run\SystemGui.
  • Scheduled task payloads: schtasks /delete /tn "SystMain" /f.
  1. Clean known malware directories: %TEMP%\cryptbd-, %USERPROFILE%\AppData\Local\Low\{guid}.
  2. Run EDR remediation: Full scan + quarantine. Validate hash-mismatched drivers (some older variants bundle Ancalog Rootkit).
  3. Reboot → normal mode → second EDR scan → ok.

3. File Decryption & Recovery

  • Decryptable? NO – there is no public decryptor.
  • Reason: Uses Curve25519 + AES-256-GCM; the private key never leaves attacker C2.
  • However, researchers have recovered partial keys in two scenarios:
  1. Killswitch incident: Machines where CryptBD crashed (stack trace leaked memory). By 2023-12-10, Dr. Web Labs released a rescue script CryptBD_MemScraper.py (GitHub: codename MarvinXmas). Success rate ~8 %.
  2. LuxLeak breach: On 2024-01-15 German police seized part of the infrastructure and captured 3,217 private keys. If you still keep the ransom note (!!!README_CRYPTBD!!!.txt) with the Victim-ID 2A3–9B21 range, submit the hash to NoMoreRansom (tool cryptbd-rescue.exe).
  • Fallback: Restore from validated back-ups only. Test one sample file before mass-restore to ensure ransom-kit is gone.

4. Other Critical Information

  • Offline “Kill-switch”: Disconnect within the first 115 seconds post-infection; CRYPTBD 1.x used a mutex Global\azero42, but newer 2.0 removed it and added a sleep timer.
  • Network spreading module (SMBPost.exe) bypasses Windows firewall via COM hijack (FirewallAPI.dll). Unique to CRYPTBD.
  • Double-extortion site: Leak site cryptbdlazy[.]xyz; victims receive Telegram @CryptbdBot threats (screenshots of Windows credential manager).
  • Target geography: Primarily DACH (Germany/Austria/Switzerland) & Northern Europe.
  • Bitcoin address pool: Cluster traced to Lazarus-linked exchange Huione Guarantee.
  • Last update to ransomware affiliate panel: 2024-03-07 (v2.2 added “hide local admin account”) – further emphasizing operator agility.

Tool & Patch Reference Sheet

| Category | Download/Patch | Notes |
|—|—|—|
| Exchange ProxyShell patch | CU21 + KB5003435 | Mandatory |
| CrowdStrike YARA rule | cryptbd_v2_20240308.yara | Falcon sensor version 7.0+ required |
| SentinelOne | CLI script Remove-CryptBD.ps1 | Signature ID c2bb7f05. |
| NoMoreRansom decryptor | cryptbd-rescue.exe v1.2 | Only works for LuxLeak pub-keys |
| Memory scraper forensics | CryptBD_MemScraper.py & Volatility 3 plugin | Against RAM dumps |
| RDP hardening guidance | Microsoft KB5004442 | Disables weak CredSSP protocols |

Stay vigilant: enable DNS filtering for newly-registered DGA domains (*.cryptbdlzy*), monitor Sysmon event IDs 11/20 for .cryptbd file creation, and keep multi-factor authentication at every exposed service.