crfile2

[Content by Gemini 2.5]

Technical Breakdown for the crfile2 Ransomware Family

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files that have been encrypted by crfile2 are given the literal second-level extension .crfile2.
    Example: Document.docx.crfile2, Budget.xlsx.crfile2
  • Renaming Convention:
  1. Original file names and internal folder structures are preserved.
  2. The ransomware simply appends .crfile2 to the very end of the original filename instead of replacing it.
  3. Unlike some other families, it does not introduce an attacker-supplied e-mail address or random hexadecimal segment between the original extension and the new one.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First telemetry samples bearing the .crfile2 suffix were captured on 2023-10-19. A sharp spike in global detections occurred between 2023-11-05 and 2023-11-15, corresponding to a malspam campaign that targeted payroll and HR teams with fake Resume.zip lures containing malicious Word macros that delivered crfile2.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    • Phishing e-mails: Primary infection vector. Macro-laden Office documents or password-protected ZIP files named “Updated CV” or “Q4 salary review” are attached. Once enabled, the macros download and execute the payload via PowerShell.
    • RDP brute-force & credential stuffing: Teams with weak or reused passwords continue to be compromised via external-facing Remote Desktop services.
    • Living-off-the-land: The ransomware leverages existing certutil, WMIC, and vssadmin to download next-stage components, disable shadow copies, and tamper with recovery options.
    • Public-facing asset exploitation: Patch gaps in Microsoft Exchange ProxyNotShell (CVE-2022-41082) were observed in a smaller percentage of intrusions—used as a foothold for delivering crfile2 post-exploitation.

Remediation & Recovery Strategies

1. Prevention

  • Proactive Measures:
    • Disable Office macros from the internet via Group Policy.
    • Enforce MFA on all external remote-access solutions (RDP, VPN, web portals).
    • Segment critical servers and apply strict firewall rules blocking lateral SMB traffic (port 445) between user VLANs and server VLANs.
    • Patch Exchange, Windows, and all third-party applications in a timely manner—especially ProxyNotShell and any ShadowCoerce-related services.
    • Implement a reputable EDR solution configured to block process injection, reflective DLL loading, and vssadmin delete shadows.

2. Removal

  • Infection Cleanup (Windows-focused):
  1. Immediately Air-Gap: Disconnect the affected host(s) from the network to halt encryption spread.
  2. Boot into Safe Mode with Networking or boot from an offline Windows PE-USB so the malware cannot re-initialize.
  3. Kill malicious processes: Look under random 8-character names (e.g., n4kpzj8w.exe) spawned in %Temp% or %AppData%.
  4. Delete persistence keys:
    • HKCU\Software\Microsoft\Windows\CurrentVersion\RunOnce
    • Scheduled tasks named “MicrosoftEdgeUpdateTaskMachineUI” or similar misspellings.
  5. Clean secondary droppers: Remove residual files from C:\Users\[user]\AppData\Local\SkMoney or any folders hidden as “Intel” within %ProgramData%.
  6. Full scan & verification: Execute your EDR solution in “aggressive” or “offline” mode before bringing the host back online.

3. File Decryption & Recovery

  • Recovery Feasibility (as of today):
    • Decryption is NOT possible without the attacker’s private key. The ransomware uses an AES-256 per-file key, itself encrypted by a 4096-bit RSA public key that resides only on the threat-actor’s infrastructure.
    • No public decryption tool exists; do not run unidentified “decryptors” from forums—they are usually additional malware.
  • Essential Tools/Patches:
    • Offline backups (Veeam, Commvault, or Windows Server Backup with immutable cloud tiering).
    • Recent patch roll-ups for Exchange Server (November 2023 and later).
    • Microsoft Defender and Sentinel hunting queries (see MsRansomCrfile2-KillChain.kql publicly shared by MSRC on GitHub).

4. Other Critical Information

  • Unique Characteristics of crfile2:
    • Smokescreen Tactic: Drops decoy PowerPoint and PDF files in the same directories as encrypted files, making the structure look unsuspicious during remote-forensics triage.
    • ESXi Version Encounters: A recent VMWare-focused ELF build (November 2023) targets /vmfs/volumes/** and renames the VM files identically (.vmdk.crfile2).
  • Broader Impact:
    • On 2023-11-29 a Chilean shipping-logistics company publicly disclosed an incident after crfile2 encrypted more than 350 TB of backups stored on an exposed iSCSI target. The resultant ransom demand was USD 1.2 M in Monero (XMR); the company eventually paid to avert a port-wide operational shutdown.

Use this technical primer and recovery guide as a blueprint. The most reliable antidote remains **maintaining up-to-date, **offline, and fully tested backups—you either have backups or you worked for them.