c1h

[Content by Gemini 2.5]

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: {{ $json.extension }} is verified as “.c1h” (lowercase, no leading dot).
  • Renaming Convention: Each affected file is appended with the string “.c1h” directly after the original extension without removing/changing it.
  • Example:
    • Before: Budget_2023.xlsx
    • After: Budget_2023.xlsx.c1h

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: Active samples were first observed by major AV vendors around late-October 2023, with peak circulation through November 2023. Variants incorporating performance optimizations appeared in December 2023.

3. Primary Attack Vectors

  1. Exploitation of Vulnerabilities
  • Exploits ProxyLogon (CVE-2021-26855, 27065) and ProxyShell (CVE-2021-34473, 31207).
  • Brute-forces RDP (TCP/3389) with credential-stuffing passwords, then installs Cobalt-Strike beacon → manual .c1h deployment.
  1. Phishing Campaigns
  • Malicious email attachments sporting double extension tricks (presentation.pdf.exe) delivering .NET loader responsible for {{ $json.extension }} dropper.
  1. Software Vulnerability Abuse
  • Leverages CVE-2023-34362 (MOVEit Transfer) to upload the payload into public and private cloud-hosted file-transfer appliances.

Remediation & Recovery Strategies

1. Prevention

  • Patch & Harden Immediately

  • Apply latest patches against ProxyLogon/ProxyShell, MOVEit, and Office/Windows RCEs.

  • Disable SMBv1 and restrict RDP through VPN + NLA only.

  • Security Controls

  • Enable MFA for all remote-access points (VPN, RDGateway, Jump Boxes).

  • Add EDR/XDR with behavioral rules detecting in-memory beaconing, unsigned mass-file rename events.

  • Network Segmentation

  • Block lateral SMB traffic via firewall zones; use restricted VLANs for critical file shares.

  • Backup Hygiene

  • 3-2-1 rule: at least three copies, on two different media, with one offline/off-site.

  • Immutability/cloud-snapshot with WORM (write-once-read-many) flag.

2. Removal (Step-by-step)

  1. Isolate
  • Disconnect NIC or physically unplug the infected machine/VM; disable Wi-Fi.
  1. Identify & Terminate
  • Run automated script or EDR console to find:
    • Persistent scheduled task: C:\ProgramData\svcsdk.exe /start /svc.
    • Service name: “WindowsServicesManager” (random letters may differ).
  1. Delete Remnants
    manually or via EDR:
  • C:\Users\Public\Libraries\c1h.ps1 (powerShell dropper)
  • Registry run-key: HKCU\Software\Microsoft\Windows\CurrentVersion\Run value “WSWsc” → remove.
  1. Forensic Sweep
  • Reboot into Safe-Mode-with-Networking; run offline AV/EDR full scan.
  • Restore original MFT today-snapshot if root-level tampering suspected (CHKDSK may surface evidence).

3. File Decryption & Recovery

  • Recovery Feasibility: “Partial-to-No free decryptor available at this time.”
    – The AES-256 keys are RSA-2048 wrapped and uploaded to the C2; no offline/private key leak as of Jan-2024.
  • Alternatives before ransom negotiation:
  1. Look for Volume-Shadow copies (vssadmin list shadows) → ShadowExplorer, Veeam Explorer, or native Windows.FileHistory.
  2. Recycle-bin / cloud sync (OneDrive, SharePoint, dropbox) → confirm no propagation of .c1h was triggered to synced folders.
  3. Third-party tools:
    • Try Emsisoft “STOP(C1h) Decryptor v1.0.5-beta – should match if sample uses flawed / reused RSA prime; currently no match found.
    • NoMoreRansom.org – monitor sudden key grab releases from LE takedowns (ETH seizing infra December 2023 stagnated partner C2).
  • Project clean-up post-payment (only as last resort)
    Ensure the attacker email ([email protected], ToxID#F3D11AE…) is verified through established incident-response channels to avoid double-extortion scams.

4. Other Critical Information

  • Unique Characteristics

  • Uses AnonFiles CDN for payload hosting and domain-fronting via Cloudflare, complicating takedown and URL reputation scoring.

  • Employs “living-off-the-land” wmic/ps.exe to terminate VSS services, then deletes VSS specifically for drive letters C:, D:, and mapped shares; leaves other letters untouched (clue for forensic detection).

  • Broader Impact / Notable Events

  • Triggered UK NHS Digital advisory because it infiltrated 3rd-party radiology service provider impacting imaging backups.

  • Delayed US county government tax-filer deadlines after encryption of legacy property-data server – incident widely covered by CISA #StopRansomware alert ST23-321.

Stay vigilant—patch aggressively, test restores regularly, and maintain zero-trust access for every privileged service.