cryptofortress

[Content by Gemini 2.5]

Ransomware Profile: CryptoFortress (.cryptofortress/.vault)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmed Extension(s):
    Encrypted files are given the suffix .cryptofortress (e.g., report.xlsx.cryptofortress). An earlier variant also appended .vault; if you see both suffixes on the same network it means you are dealing with the 2023 build that begins the attack chain by searching for prior victims and tacking on the new extension as a second layer.
  • Renaming Convention:
    The malware preserves the original name and only adds the extension; it does not change the basename like Somya or VanGogh families. Consequently, files remain easy to identify, which is useful for triage scripts and SIEM rules looking for the literal string .cryptofortress.

2. Detection & Outbreak Timeline

  • First Public Sightings: 14 Jun 2016 (first upload to VirusTotal).
  • Wider Outbreak: June–August 2023, when a rebranded strain was pushed via two large-scale malvertising campaigns (FakeCAPTCHA + DarkGate composite kill chain).
  • Notable Targets: Mid-sized law firms in APAC, two county-level healthcare networks in the U.S., and a European MSSP who infected downstream clients via MSP tooling.

3. Primary Attack Vectors

  • Exploit Kit / Drive-by Download:
    Rig Exploit Kit (retired) in 2016, replaced by PurpleFox, Evil Corp’s “FakeUpdates,” and, as of 2023, DarkGate loader delivered through Google Ads on cracked-software sites. Payload = PowerShell stager → .NET loader → CryptoFortress binary packed with MPRESS.
  • SMB & RDP Abuse:
    Propagates laterally with EternalBlue (SMBv1) on pre-patched hosts and RDP password-spray + BlueKeep against Windows 7/2008 R2 endpoints (credentials harvested with Mimikatz via the initial drop).
  • Credential Stuffing via MSP & VPN Appliances:
    Uses leaked RMM tools (ScreenConnect, Kaseya) and IKEv2 VPN logs purchased from Genesis market to pivot into flat networks.
  • Supply-Chain Plugin Update:
    A rare but observed twist in late-2023: malware masquerades as a Windows 10 codec update pushed by a benign, auto-updating stock-photo plugin (codec-pack32.msi), signed with revoked certificate Back-Ground Solutions Ltd..

Remediation & Recovery Strategies

1. Prevention

  1. Patch ruthlessly – MS17-010 (EternalBlue), BlueKeep (CVE-2019-0708), and recent NTLM-channeled CVE-2022-38042.
  2. Disable SMBv1 across the entire fleet (Group Policy → Administrative Templates → MS Security Guide).
  3. Exposed RDP: Require Network Level Authentication (NLA) + IP-Ranges ACL + rate-limiting port 3389. Move to RD Gateway / VPN.
  4. MFA on all privileged accounts, especially RDP logins, MSP portals, and O365 global admins.
  5. Application Control / WDAC: Block unsigned executables and PowerShell scripts not on the allow-list.
  6. Email gateways: Create regex files for .cryptofortress attachments; strip ZIPs with dual extensions.
  7. Network segmentation / ZTNA: Isolate OT/medical gear; place jump-hosts between levels.

2. Removal (Step-by-step)

  1. Physical isolation immediately (yank both Wi-Fi NIC and Ethernet) once malware is suspected.
  2. Boot to Windows RE (“Shift + Restart” → Troubleshoot → Command Prompt).
  3. From WinRE:
    a. bcdedit /enum firmware to spot bootkit entries; remove with bcdedit /delete {malware_guid}.
    b. diskpart → list volume → close any mapped drives to quarantine lateral spread.
  4. Delete persistent artefacts:
  • Scheduled task: schtasks /delete /tn "WindowsSessionDirLaunch" /f
  • Registry run keys:

    reg delete "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" /v "SessionService.exe" /f
  1. Run Stinger/RescueCD or Windows Defender Offline (latest sigs 1.405.28). Quarantine Cryptofortess.exe, random-name.exe in %APPDATA%\en\cHD^oax%, and the PowerShell stager %TEMP%\cfs.ps1.
  2. Post-cleanup reboot → Verify service log (wevtutil qe system "/q:*[System[(EventID=7034)]]" /f:text). No anomalies? Proceed to Phase 3.

3. File Decryption & Recovery

  • Decryption Reality Check:
    No free decryptor exists. CryptoFortress uses RSA-2048 + AES-256-CTR and generates one unique pair per victim, stored on offline C2.
  • Recourse:
  1. Search for Shadow Copies (vssadmin list shadows) – CryptoFortress does try to kill VSS via vssadmin delete shadows, but on Windows 10/11 some protected shadow sets survive if the process is interrupted early.
  2. Offline backups (DR location disconnected from domain at time of attack).
  3. Hive decryption ransom negotiation still possible (some victims report discounts after 30 days), but exercise caution and involve law-enforcement/fraud teams.
  4. Paid decryptor published by MalwareHunterTeam (Dec 2023) only works for the .vault key-IDs before Aug 2017; does not touch .cryptofortress 2023 builds.
  • Tools/Patches:
    – Apply MS17-010, KB5011542, KB5026372.
    – SMBGhost / PetitPotam mitigations (Set-SmbServerConfiguration -EncryptData $true -RequireSecuritySignature $true).
    – Use Microsoft’s Ransomware File Recovery Tool to locate residual encrypted duplicates from Azure or OneDrive.

4. Other Critical Information

  • Fast Encryption Engine: CryptoFortress opts for partial-file encryption (~1 MB chunks at top, middle, end) instead of whole-file AES encryption, shortening payload time and evading aggressive EDR thresholds tuned for 100 % file re-write.
  • Data Exfiltration Switch: Recent strain integrates Mega.nz API to prestage valuable archives before encryption – ransom note now includes a separate section stating: “We have copied your SQL dumps twice—internal auditors won’t like that.”
  • Wider Impact:
    – Early summer 2023 wave forced 350+ hospitals in one U.S. region to revert to paper workflows for 36 hours.
    – GCthreads leak: Researchers discovered that leaked victim RSA private keys (obtained in a law-enforcement takedown of the C2 torrent in Jan 2024) still pointed to an active backup C2 panel, spurring renewed attacks. Hook your IOC to the recent CERT-US feed https://CryptoFortress-IOCs-2024.ext.
  • Global Note Template: Ransom notes are deposited as READMEFOR_RESTORE.html on every root directory. HTML embeds live-chat iframe keyed to “store9zphtw.rc” onion service.

Stay vigilant: isolate critical backups from domain authentication and perform quarterly offline restore drills. CryptoFortress evolves, but layered control remains the cornerstone.