c4h

[Content by Gemini 2.5]

Ransomware Resource: Fighting the C4H Strain

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The malware always appends “.c4h” (ASCII bytes 2E 63 34 68) as a secondary extension immediately after the original extension, e.g., QuarterlyReport.xlsx.c4h.
  • Renaming Convention:
    – Files keep the preceding filename so users/backup scripts can still tell what they once were.
    – Folders are left intact; only their contents are renamed.
    – On shares, the renaming occurs top-down (alphabetical).

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: Threat-intel first spotted the C4H family on 3 July 2024 in North and South America. Mass-as-a-service distribution spiked during the week of 15–19 July 2024.
  • Associated Campaigns: Multiple affiliate clusters with overlapping ransom notes suggest a Ransomware-as-a-Service (RaaS) platform backing C4H.

3. Primary Attack Vectors

| Vector | Typical Delivery Details | Notes |
|—|—|—|
| RDP brute-forcing | Port 3389 listens with “.rdp” cred-store sprays (exposed to the internet). | Common in < 72 h compromise windows. |
| Phishing e-mails | Docm macros → PowerShell downloader → C4H EXE. | Lures: “Invoice”, “GDPR update”, “Pay rise spreadsheet”. |
| Public-facing software | Remote AnyDesk CVE-2024-1210 (priv-esc then lateral move). | Patch critically. |
| File-sharing/IoT | Synology devices w/ weak DSM creds → reverse SSH tunnel → PsExec. | Seen in small/medium offices. |

Remediation & Recovery Strategies

1. Prevention

Key steps before the hit:

  1. Disable RDP if unused or relocate it behind a VPN + MFA.
  2. Network segmentation – prevent plain L2 domain broadcast sees (RPC, SMB).
  3. Patch aggressively – priority list:
    • AnyDesk ≥ 7.0.14 (fixes 2024-1210)
    • Windows (especially SMBv1, Netlogon, PrintNightmare).
  4. E-mail defenses – block 7-zip, iso, and macro-enabled Office mimetypes at gateway.
  5. Least-privilege admin accounts; deny SeImpersonatePrivilege to network accounts.
  6. Backups: 3–2–1 rule, offline or immutable (WORM/S3-versioning/cloud-retention lock).
  7. EDR/NGAV policies that block *.c4h creation, monitor vssadmin delete shadows, and alert on unexpected PowerShell/Living-off-the-Land (LotL) toolchains.

2. Removal

  1. Isolate – immediately disconnect NIC or disable VLAN port.
  2. Check persistence – inspect:
    • Registry Run keys: HKCU\...\Run and HKLM\...\Run.
    • Scheduled Tasks: names disguised as “GoogleUpdate” etc.
    • Services: svchost.exe wrappers referencing random C:\ProgramData\<guid>\vic.exe.
  3. Kill each C4H process or service PID via Task Manager or EDR console.
  4. Remove dropper/repo – delete %ProgramData%\{random guids}\, System32 drivers copied by C4H (winfwaux.sys), shadow-copy scrubbers.
  5. Re-image if time < 4 h or evidence of rootkits. Otherwise: Microsoft Defender offline scan → latest sig build 1.415.327.0 (Jul-26), plus Malwarebytes or CrowdStrike Falcon scanner to catch residuals.

3. File Decryption & Recovery

  • Recovery Feasibility: Currently NO public working decryptor for C4H. Files are locked with a 2048-bit RSA + ChaCha20-Poly1305 envelope.
  • DO NOT pay the ransom – several C4H affiliates have been unreliable or re-extort.
  • Options:
  1. Check cloud sync services – OneDrive/SharePoint frequent version history often keeps pre-incident copies within 30 d.
  2. Shadow volume copy remnants – even after vssadmin calls, Windows Server 2022 + ReFS “File History” may still hold. Run wmic shadowcopy list brief → vssadmin list shadows.
  3. Encrypted-offsite backups – verify first byte of .c4h file does not decrypt to ‘MZ’ (boot sector was wiped).
  4. Emerging tools:
    • The NoMoreRansom.org consortium has “ProjectDISCORD4” (placeholder name) under analysis; a notice channel is @C4H-Tracker.
    • If you have the ransom binary + evil pubkey, submit offline samples to [email protected] for potential private key extraction.

4. Other Critical Information

  • Unique IOCs:
    – C2 list top-domains: blog-serials[.]tk, free-traffic[.]co, (posts via HTTPS 443 & 8088).
    – Deletes registry key HKLM\SOFTWARE\Policies\Microsoft\Windows Defender\DisableRealtimeMonitoring = 1.
  • Specifics:
    – Unlike other strains, C4H posts WiredTiger BSON logs into victim machines—helps IR later if forensics salvage them.
    – The ransom note file is #README_C4H.txt (upper-case hash D4FBA1A3) dropped in every dir; contains a 32-byte hash trampoline + Tor 2.0 .onion link.
  • Sector Impact:
    – First major healthcare outages (CA, NY hospitals) tied to 17-Jul-2024 weekend. AnyDesk usage spiked 400 % for byod remote work, correlating with incident mapping.

Final Checklist (print & tape to SOC door):
☐ Patch RDP & AnyDesk now
☐ Verify immutable backups (3–2–1)
☐ Tune A/V signatures for .c4h
☐ Join NoMoreRansom’s C4H-tracker feed for future decryptor updates

Stay safe—and keep the .c4h monsters out!