cryfile

[Content by Gemini 2.5]

Comprehensive Guide: CYRFILE Ransomware

(victims may first notice the file extension “.cryfile” appended to every encrypted file)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The ransomware uses “.cryfile” (lowercase).
  • Renaming Convention:
    Original → Picture.jpg.cryfile
    Pattern: OriginalName.OriginalExt.cryfile
    No additional prefixes or random hex strings are prepended, keeping filenames short but instantly identifiable.

2. Detection & Outbreak Timeline

  • First Public Sightings: Early 2021 (dark-web forum advertisements + leaked chat logs).
  • Wider CPRs (Cyber-Public Reports): April 2021 spike after a large-scale phishing wave masquerading as FedEx invoice alerts.
  • Subsequent Resurfaces: Sporadic winter-autumn 2022 campaigns using updated phishing templates (“PayPal dispute”, “Virtual Event Hosting details”).

3. Primary Attack Vectors

| Vector | Details & Real-world Examples |
|——–|——————————-|
| Spear-phishing emails | ZIP → .ISO → .cmd or .js downloader that fetches payload from Discord CDN. |
| Unpatched SonicWall SMA or Fortigate VPN appliances | attackers scan for CVE-2020-5135 & CVE-2021-20016, drop reverse shell, then hand-off to cryfile executable. |
| Weak or re-used RDP credentials | Brute-force login lists from prior breaches; once inside, a PowerShell drop-script fetches cryfile from a legitimate-looking Azure blob (e.g., “blob.core.windows.net/officefiles/update.exe”). |
| Pirated software bundles | Masquerades as “Adobe Photoshop 2022 crack.exe”; hidden SFX archive runs cryfile payload in silent mode. |
| Software supply-chain helper scripts | NPM code-injection adware (group “LimeSpark”) installs cryfile on build servers. |

Remediation & Recovery Strategies

1. Prevention

  1. Patch aggressively
  • Windows OS (SMBv3 patches)
  • VPN appliances (FortiOS, SonicWall SMA)
  • Remote Desktop Services (RDP Gateway & NLA)
  1. Disable macro & ISO auto-run via GPO: 
   Set-ItemProperty -Path "HKCU:\Software\Microsoft\Windows\CurrentVersion\Policies\Attachments" -Name "SaveZoneInformation" -Value 1

  1. MFA on all outward-facing services (RDP, Citrix, VPN, Exchange), including internal jump-servers.

  2. Email gateway rules to quarantine or rename .ISO, .IMG, .RTF, .HTML (ISO-inside-ZIP attachments).

  3. Application whitelisting via Windows Defender Application Control or a capable EDR—block execution of %TEMP%\*.exe, %USERPROFILE%\Downloads\*.ps1 unless signed.

2. Removal

  1. Isolate: Physically pull LAN cable, disable all Wi-Fi adapters.
  2. Identify: Check Job Scheduler (schtasks /query), Run registry keys (HKLM\…\Run) for suspicious autorun (random filename like update5153.exe).
  3. Boot into SafeMode with Networking → Full scan with Malwarebytes + Kaspersky Rescue Disk or Windows Defender Offline.
  4. Credential reset on every user + service account discovered on the same subnet (Ntdsutil or LAPS helps).
  5. Remove persistence: 
   Remove-ItemProperty -Path "HKLM:\Software\Microsoft\Windows\CurrentVersion\Run" -Name "WindowsServiceUA" -Force
   Remove-Item -Path "$env:APPDATA\Microsoft\Windows\Start Menu\Programs\Startup\cryptodesktop.exe" -Force
  1. Patch updated hosts, then bring back online.

3. File Decryption & Recovery

  • Current Status (Up-to-the-hour): No publicly available decryptor.
    Cryfile uses 2048-bit RSA + ChaCha20 in stream mode, with the private key stored only on the attacker’s server.
  • Known Attempts:
  • Kaspersky “RakhniDecryptor”, Emsisoft — no support added (format signature differs).
  • Brute-force of 2048-RSA is computationally infeasible.
  • Recovery Remedies:
  1. Offline backups (3-2-1 rule) → quickest and cheapest.
  2. Shadow-copy & VSS (vssadmin list shadows) — cryfile wipes “\System Volume Information\” but sometimes misses OneDrive/SharePoint recycle bin.
  3. File-only recovery tools: PhotoRec or DiskDigger for raw carving after re-imaging drives.
  4. Negotiation strategy: threat actors maintain a ticket system in TOR (.onion site). Median paid ransom in 2023 logged at US$29 000 (Bitcoin). Local laws and corporate policies should always be observed; paying is never recommended.

4. Other Critical Information

  • Unique Characteristics
  • “CryFile README.TXT” is dropped in every searchable directory; note unusual locale ids (Brazilian Portuguese & Spanish) although the ransomware is coded in C++ by a seemingly native English speaker—indicates expanding regional targeting.
  • PrintSpooler Fix Script Bait — cryfile spreads inside a fake “WindowsPrinter Hotfix.hta” post-May 2021 PrintNightmare disclosure.
  • Broader Impact
  • Healthcare centers in 2021 still running open RDP on port 3389 faced 2-week downtime.
  • One mid-size MSP ($280 M revenue) lost Active Directory domain wide when cryfile executed on a domain controller; demonstrates lateral-movement scripts are shared with some Conti TTPs (Rclone exfil, PrintUtility.dll sideloading).

| Tool / Patch | Purpose | Link |
|————–|———|——|
| MS17-010 (SMB) Security Update | Blocks EternalBlue & similar exploits | microsoft.com |
| SonicWall SMA 10.x hotfix | Fixes CVE-2021-20016 | SonicWall Security Advisory SNWLID-2021-0001 |
| Kaspersky Rescue Disk | Offline boot scan | kaspersky.com |
| Microsoft 365 Recycle Bin Tools | Restore OneDrive/SharePoint files if VSS deleted | OneDrive admin recycle-bin |

Stay vigilant—update and test your backups quarterly, and treat any unknown “.cryfile” execution attempt as a red-alert incident.