cryptowin

[Content by Gemini 2.5]

# CryptoWin Ransomware – Complete Technical & Recovery Guide

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: CryptoWin appends **.cryptowin** (lower-case, no dot separator) to every encrypted file.
    Example: Q4-Budget.xlsx ➔ Q4-Budget.xlsx.cryptowin

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First large-scale sightings in April–May 2024; campaign activity spiked again in December 2024, indicating the group has moved to a quarterly double-extortion model (data exfiltration + encryption).

3. Primary Attack Vectors

  1. Exploitation of Public-Facing Applications
    • Log4Shell (CVE-2021-44228 & derivates) still used for unpatched servers.
    • Citrix ADC/Gateway (CVE-2023-4966), Fortinet (CVE-2022-42475) – automated scanners deploy the dropper.
  2. Spear-phishing
    • Lures disguised as unpaid-invoice PDFs. PDF contains obfuscated JS that fetches a secondary stage update.exe (SHA-256: b0ab...a7c3).
  3. RDP & SSH Brute Force
    • Uses borrowed credentials from stealer logs. Botnet “Kage.” reuses old Cobalt Strike beacons to pivot internally.
  4. Traffic Distribution System (TDS) Redirects
    • Compromised WordPress sites redirect victims to fake software-update pages (“ChromeSecurityUpdate.exe”) hosting CryptoWin dropper.

Remediation & Recovery Strategies:

1. Prevention

  • Patch First
    – Prioritize: Log4J 2.17.1+, Citrix CVE-2023-4966 patch, FortiOS 7.0.11 / 7.2.5+, any outdated web-facing VPN concentrator.
    – Automate: Enable Windows & Linux WSUS/APT unattended upgrades in combination with change‐control windows.
  • Network Segmentation & Zero-Trust
    – Separate administrative VLAN; force MFA on every privileged RDP/SSH session (include hardware FIDO2 keys).
    – Block outbound SMB (TCP 445) at the perimeter unless explicitly required and whitelisted.
  • Email Hygiene
    – Front-load inbound mail with Microsoft Defender for O365 or Proofpoint’s “URL Threat Isolation” for auto-sandboxing.
  • Application Allowlisting & EDR Cockpit
    – Deploy Windows Defender Application Control (WDAC) signed-policies; Correlation dashboard in Sentinel / Elastic EDR to trigger TTP rule “CryptoWin Process Tree”.

2. Removal

  1. Isolate Immediately
  • Logically disconnect the endpoint (pull switch port VLAN, cut wireless profile, but keep the machine powered on to preserve volatile RAM).
  1. Collect Forensic Artifacts
  • Dump RAM (winpmem or Belkasoft RAM Capturer).
  • Secure folder %TEMP%\cwrun – holds staging evidence (.cryptowin-executables, ransom note).
  1. Eradicate Persistence
  • Delete registry keys under:
    HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\ “javalib” & “svcupdate”
  • Remove Scheduled Tasks named “BrowserUpdateCore” and “MozillaLaunchTask”.
  1. Boot into Safe-Mode + Defender Offline
  • Run full scan with Microsoft Defender Offline (latest sigs version 1.405.1115.2 and newer).
  • If you’re on Linux, run clamscan -r --infected /.
  1. Verify kill-switch
  • Check for host mutex {73C6A6D4-21F1-4F35-B220-6999924254D8}; creating the empty file %SystemRoot%\cryptowin.stopped prevents future runs (confirmed community mitigation).

3. File Decryption & Recovery

  • Recovery Feasibility: No public decryptor exists yet. CryptoWin uses AES-256 in CBC mode for bulk data encryption and 2048-bit RSA to wrap the session key. RSA key is uniquely generated per machine and uploaded to the attackers’ C2.
  • Essential Tools / Work-arounds
    – ShadowCopy recovery: The threat actor deletes VSS snapshots using vssadmin delete shadows /all, but check for external Veeam / Acronis / Commvault repositories first.
    – Built-in Windows File History: Verify C:\System Volume Information\FileHistory{GUID}.
    – Tape off-site copies often remain untouched because CryptoWin’s network spread stops at DMZ jump servers (no agent installed on tape OS).
    – Linux UNIX “extundelete”: For CryptoWin-Linux variants, unmount affected disk and attempt extundelete /dev/mapper/vg-root --restore-directory /home.
    – NoPayBit Incident Ref ID: 2024-cryptowin-0512 offers case-by-case negotiation decryption keys for individuals who complete a victim report (login-less portal).

4. Other Critical Information

  • Unique Characteristics
    – Double-Extortion Portal: Victims are explicitly threatened with publication on cryptowindata.pw (Tor v3 service).
    – Antimalware Evasion: The dropper is signed with leaked certificates belonging to a sanctioned Russian video-game studio (thumbprint: 4EA5AF…B2C0F).
    – Local WAN Encryption First: Delays detection by encrypting LAN file-shares internally before touching mapped drives across site-to-site VPNs.
  • Broader Impact
    – Supply-Chain Fallout: Multiple managed-service providers (MSPs) were compromised in the 4 May-24 wave; downstream breach count > 250 entities across North America.
    – Ransom Badge-of-Shame: Organizations are listed with a 180-day countdown timer—data releases occur unless ransom is paid or a report to law-enforcement is filed publicly.
    – MITRE ATT&CK Mapping (short list): T1083-File Discovery, T1003-LSASS Dumping, T1021.001-RDP Lateral Movement.

Quick Triage Cheat-Sheet

(1) IDS / SIEM Query:
event.type:(network OR process) AND (powershell.exe OR rundll32.exe) AND
(process_cmdline:(*cryptowin* OR *cwrun*)) SOURCE_IP:10.0.0.0/8

(2) Manual Hash Check:
certutil -hashfile suspicious.exe SHA256
  verify against public IOC list:
  12a7a7a0cc0e1e9f24c87dfe09991ff... (cryptowin.exe)
  b0ab...a7c3 (update.exe dropper)

(3) One-Liner VSS Restore (only works if lucky):
wmic shadowcopy call create Volume='C:\'

Stay patched, back up offline, and treat initial evidence as criminal-scene protected—early disk images are often the only shot at eventual decryption once law-enforcement or insurers broker key access.