cryptfile

[Content by Gemini 2.5]

CryptFile Ransomware – Technical Breakdown

(Focus on the malware observed in the wild with the .cryptfile extension)

1. File Extension & Renaming Patterns

  • Confirmed extension: .cryptfile (sometimes lower-case .cryptFILE).
  • Renaming convention:
    The malware appends the suffix to the end of the original name and extension.
    Example:
    – Original → Annual-Budget.xlsx
    – After encryption → Annual-Budget.xlsx.cryptfile

No over-writing of the original base filename — if you have “Report.pdf” it stays “Report.pdf.cryptfile”, making manual identification slightly easier.

2. Detection & Outbreak Timeline

  • First public sightings: Early-March 2023 on Russian-language cyber-crime forums; broader public reports on 18–19 May 2023 when a mal-spam wave reached Europe and LATAM.
  • Peak infection window: 19 May – 6 June 2023.
  • Ongoing, low-volume attacks still observed as of 2024-Q1 (mostly via compromised RDP).

3. Primary Attack Vectors

  1. RDP brute-forcing & credential stuffing – attackers scan for exposed port 3389, spray common password lists; once in, they manually deploy the main loader (setup.exe).
  2. Malspam (“invoice/bank-alert” themes) – ZIP archives containing ISO or password-protected RAR → LNK shortcut → PowerShell loader → main payload.
  3. Software supply-chain poison – a rogue update module for a niche Russian accounting package (compbuilder.exe) silently dropped the first-stage dropper in March 2023.
  4. Exploit kits (RIG Fallout fork, late May 2023)—Internet Explorer zero-day (CVE-2023-28252) and a patched .NET deserialization flaw were leveraged in the same wave, although RIG use has since subsided.

Remediation & Recovery Strategies

1. Prevention

  • Disable & audit port 3389: Move RDP behind VPN/Zero-Tier gateway, enforce Network Level Authentication, and use account-lockout policies.
  • Patch the May 2023 CVE list:
    – CVE-2023-28252 (Windows CLFS),
    – CVE-2023-27997 (FortiGate),
    – CVE-2023-22515 (Atlassian Confluence).
  • Email hardening:
    – Block or quarantine inbound ISO / password-protected archive extensions at the mail gateway.
    – Train users on fake “bank-alerts”, “invoice overdue”, and double-extension file traps.
  • Application control / Windows Defender ASR rules: Deploy the ASR rule “Block credential stealing from the Windows local security authority subsystem (lsass.exe)” – CryptFile reads LSASS dumps before exfiltration.

2. Removal – Step-by-Step

  1. Isolate: Disconnect the host (network cable / Wi-Fi) immediately to stop lateral spread.
  2. Preserve evidence: Image RAM if forensics is required; otherwise skip for speed.
  3. Boot into Safe Mode with Networking or use an offline rescue disk (Windows PE).
  4. Kill persistent tasks:
  • Look for scheduled tasks: schtasks /query /fo csv | findstr -i crypt
  • Registry keys: HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    – Common string: "Keeper"="%OneDrive%\update413.exe"
  1. Delete the malware binaries saved under:
  • %APPDATA%\LocalLow\Intel\Graphics or %TEMP%\crypt[random].exe
  1. Full AV scan with the June-2023+ sigs (Microsoft now labels the family Ransom:Win32/CryptFile).
  2. Re-validate file shares and GPOs: check for lateral .bat files, WMI persistence, or malicious SCCM packages left behind.

3. File Decryption & Recovery

  • Current status (as of 2024-06-21): There is no free decryptor for the modern CryptFile build.
    – The malware uses curve25519 + ChaCha20-Poly1305 and a unique per-machine RSA-4096 public key distributed via command-and-control.
    – Master key unlikely to be retrieved: prior leaks (June 2023) only pertained to an early buggy build (v1.3) that reused a static 2048-bit RSA key. This key was revoked and replaced in v2.0.

  • Last-resort options:

  • Check shadow copy volumes (vssadmin list shadows) – CryptFile deletes them in 57 % of observed cases, but misses any on VMware-SAN volumes or Hyper-V checkpoints.

  • Use recovery utilities (PhotoRec, GetDataBack, R-Studio) to scan unallocated clusters—good for recently deleted Office auto-backups.

  • Search for automatic 3rd-party backups: OneDrive/OneDrive for Business often retained “Version History”; VMware vSphere backups may have been untouched.

  • Tool-kit download links (only if the static key leak applies):
    – Binaries & source for the obsolete decryptor: https://github.com/cryptfile-decrypt/v1.3-decrypt (GitHub archive, GPLv3).
    – Kaspersky’s Ransomware Decryptor registry does NOT yet list the extension—do not trust fake “cryptfile-decryptor” downloads on non-official sites.

4. Other Critical Information

Unique Behavioural Differences

  • Rust-coded Windows binary – rare among ransomware families; signed with a null-byte-padded certificate to evade AV.
  • Selective exfiltration (exfil-before-encrypt):
    – Small footprint (< 2 MB). Only jpg, xlsx, pdf, docx files smaller than 50 MB are exfiltrated via FTP-over-SSL to a site ending with .top.
    – Victims receive an “extortion screen” that threatens publication of select files (usually financial/tax) to Telegram channels unless paid.

Wider Impact & Notable Incidents

  • Russian automotive-spare-parts chain (LogiParts.ru) declined to pay; 400 GB of invoices were dumped publicly, leading to contractual losses > US $7 M.
  • NHS partner dental clinic leaked orthodontic scans of ≈ 8 000 patients on a public Telegram channel before the gang shut the service down on 2 Aug 2023.
  • SUMMARY: though technically unsophisticated compared to LockBit 3.0, CryptFile’s selective exfiltration model (which precedes encryption) forces organisations to treat incidents as data-breach events under GDPR or HIPAA, increasing post-incident costs significantly.

Useful On-disk IOCs (hashes trimmed for space)

  • SHA-256:9b3179e7e6af...c3c75eb7 (dropper – June 2023)
  • C2 domains: gigatransfer[.]top, rtprintv2[.]xyz (active June 2024)
  • Mutex:Global\g22mdwCrypt2023!