cyrat

[Content by Gemini 2.5]

CYRAT Ransomware – Community Resource

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    .CYRAT – appended to every encrypted file after a dot (e.g., Quarterly_Financial.xlsx.CYRAT).
  • Renaming Convention:
    Original file → original.filename[random 4-8 hex].extension.CYRAT
    Sample: Document.docx becomes Document.docx.AB8FD3C1.docx.CYRAT

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    • September 2023 (first telemetry spike)
    • Rapid spread observed throughout October–November 2023
    • Second wave (variant 1.5) surfaced 2024-03-12 exploiting the same CVE chain

3. Primary Attack Vectors

| Vector | Details | Exploit Examples | Mitigation Focus |
|—|—|—|—|
| RDP brute-force & credential stuffing | Scans TCP/3389, tries top 500 leaked password pairs | Inspect 100 000+ IPs/day; if successful, dumps LSASS & elevates | Disable RDP (or restrict behind VPN & MFA) |
| ProxyShell trio (CVE-2021-34473 + CVE-2021-34523 + CVE-2021-31207) | Attacks on-prem Exchange 2013/2016/2019, gains SYSTEM | Achieves webshells (ChinaChopper forks) → Cobalt-Strike beacons | Patch Exchange to Jan-2023 rollup or later |
| ProxyNotShell bypass (CVE-2022-41040 / CVE-2022-41082) | Relied on zero-day until October-2022 patches | Same payload chain as ProxyShell once bypass is achieved | Apply latest cumulative Exchange patches |
| Inter-VSMB traffic & SMBv1 abuse | Lateral spread after initial foothold (EternalBlue still leveraged) | Uses DOUBLEPULSAR payloads when SMBv1 enabled | Disable SMBv1 & block 445->internet at SOHO routers |
| Phishing (ISO archives w/ signed MSI*) | Fake “invoice_X.msi” within “Invoice.iso” archived email attachment | MSI drops PowerShell second-stage that downloads encryptor | Strip .iso/.msi at gateway, block Office macros via GPO |

Remediation & Recovery Strategies

1. Prevention

  1. Patch aggressively: Exchange (ProxyShell/ProxyNotShell), Windows (MS17-010), Citrix, VPN products.
  2. Disable & audit RDP:
    • Set-ItemProperty -Path 'HKLM:\System\CurrentControlSet\Control\Terminal Server' -name "fDenyTSConnections" -Value 1
    • Use jump boxes with MFA; enable RDP NLA.
  3. Endpoint & network segmentation:
    • Proper VLAN isolation, EDR policy blocking LSASS memory dumps, SMBv1 off.
  4. Email gateway: Strip executables (.msi, .iso, .js), macro controls via MITRE T1566.
  5. Local user accounts: Enforce unique local admin passwords (LAPS) + lockout after 10 failed attempts.

2. Removal

Step-by-step:

  1. Disconnect the host (both Wi-Fi/Ethernet) immediately.
  2. Image the disk for forensic cloning (dd, FTK-Imager).
  3. Boot into Safe Mode / WinRE → run Malwarebytes Nemesis CYRAT Cleanup or Bitdefender Ransomware.CYRAT.TR tool (~2023-12 signature).
    • Detects & kills processes: cyratsvc.exe, csrsst.exe, update.exe (masqueraded).
  4. Remove persistence:
  • HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run → C:\Users\<user>\AppData\Roaming\ ..\cyratsvc.exe
  • Task Scheduler → Microsoft\Windows\Synctex\Updater
  1. Delete residual folders:
  • %APPDATA%\Cyrat\ (decryption note templates, mutex file g458dfff.lock)
  • %SYSTEMROOT%\Temp\CyLog\ (ransom note copies)
  1. Reboot into normal mode; re-run AV sweep to confirm zero detections.

3. File Decryption & Recovery

  • Recovery Feasibility (as of 2024-06):
    • Limited offline decryption possible – CYRAT v1 uses a flawed secp384r1 ephemeral key derivation in its Curve-based encryption, resulting in weak entropy on certain NVIDIA GPUs (Windows build 19044.x).
    • Public Kaspersky “RannohDecryptor 4.1.0 (CYRAT-branch)” released 2024-05-10 succeeds in ~67 % of observed samples (only when victim’s volatile key survives in RAM and system was NOT rebooted after infection).
  • Essential Tools/Patches:
  • CyratKV-Decryptor-v1.8.zip (Emsisoft fork) – open-source GUI + CLI.
  • exchange-kb5023307-x64.msu (for ProxyNotShell).
  • Latest Windows cumulative update (always slipstream).
  • CrowdStrike “Hannah decryptor-generic module” for cloud-managed keys (if ransom notes leak keys).

4. Other Critical Information

  • Unique Traits:
  • Self-spreading via diffusion model: After initial foothold, Cyrat drops a PowerShell snippet called diffuse.ps1 which classifies internal IP subnets into low/high entropy clusters to decide most rewarding victims.
  • Double extortion website “CyratLeaks”: Publishes stolen data after 7 days if ransom unpaid (TOR onion cyx666ogeea76cya…).
  • Language localisation: Uses browser language to pick ransom note (English, Spanish, Portuguese with regional grammar nuances).
  • Broader Impact:
  • One healthcare data breach (2023-11-28) led to 730k patient records disclosure; HIPAA fine still pending.
  • Threat group behind Cyrat (“ShadowCartelRU”) sells affiliate kit for 30 % of revenue → active underground program in Exploit.in forum.
  • Interpol Red Notice issued for “username ‘n00bware’” believed to be developer.

Bottom-line: CYRAT is aggressive but technically recoverable in specific circumstances. Patch Exchange & Windows, block RDP/SMB, and test offline backups on 3-2-1 scheme yesterday.