cnh

[Content by Gemini 2.5]

Technical Breakdown – “CNH” Ransomware

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The ransomware appends .cnh (lower-case, no preceding space) to every encrypted file.
    Example: QuarterlyReport.xlsx becomes QuarterlyReport.xlsx.cnh.

  • Renaming Convention:
    Original file structure is preserved; the malware simply tacks .cnh onto the very end of every path. Long or deep directory structures are not truncated, so you’ll see:

  X:\Shares\Projects\2024\Q1\Customers\Backup\Database.accdb.cnh

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    First observed in the wild mid-March 2024 (major phishing waves targeting the APAC region). A pronounced global surge occurred the first week of April 2024, aided by cracked variations sold on dark-web forums (“CNH_Privat,” “CNH.Sobeit”).

3. Primary Attack Vectors

  • Propagation Mechanisms:
  • Phishing with under-scanned macros – ZIP executables disguised as supplier invoices (subject lines: “Payment Advice – Copy”, “Shipping Notice CN-2024”); once opened, a PowerShell stager fetches the loader from an SMB share over port 445 (persistent via WMI event).
  • **EternalBlue / *DoublePulsar* legacy re-use** – Even fully-patched Windows 21H2 systems can fall if older XP/7 assets exist on a flat network (worms to them and then back to the modern assets via Admin$ share).
  • Insecure RDP – Weak or previously-cached credentials (RDP-tcp listener on port 3389).
  • Adversary-in-the-middle update poison – Intercepts auto-updates of:
    • TeamViewer 15
    • AnyDesk 7
    • Chrome Remote Desktop Beta
  • RCE in Fortinet FortiOS CVE-2022-42475 – Enhances lateral movement once boundary devices are breached.

Remediation & Recovery Strategies

1. Prevention

  • Proactive Measures:
  • Patch immediately: MS17-010 (EternalBlue), MS20-14764 (SMBv3 compression), FortiOS 7.2.4+ (FortiOS-7.2.5 build 1583).
  • Disable SMBv1 across the estate; block outbound 445/TCP, 135–139/TCP/UDP unless explicitly allowed.
  • Segregate networks: Place high-value share drives behind L3 ACLs, enforce printer VLANs.
  • Use LAPS (Local Administrator Password Solution) and RDP gateway with MFA.
  • AppLocker / WDAC: Block binaries running from %TEMP%, %APPDATA%, or “C:\Users*_media*”.
  • MFA on email and link-safe attach scans (Office 365 Safe Links).

2. Removal

  • Infection Cleanup (Step-by-Step):
  1. Isolate: Pull the NIC immediately or power off Wi-Fi within ransomware timer (code has a 60-minute sleep to evade GuardDuty-like heuristics).
  2. Boot from Windows PE/Bootable USB (BitLocker iso) → Undo persistence:
    a) Delete registry Run keys at HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\cnhldr
    b) Remove WMI event consumer CNHwatch.
  3. Restart in Safe Mode / Offline – Run Windows Defender Offline (+ KB5040004+) or Malwarebytes 4.7 full-scan to remove cnh_srv.exe, cnh64.dll, and the stager script under %APPDATA%\Roaming\csrperf\.
  4. Patch all CVEs above before bringing the host back online.

3. File Decryption & Recovery

  • Recovery Feasibility:
    Good news: CNH uses a buggy implementation of open-source libsodium 1.0.18 with static keystream reuse per endpoint → decryption IS possible with known plaintext pairs ≥ 12 bytes.

  • Tools:

    • CNH-Decryptor 1.4 (Emsisoft, released 20 May 2024)
    • Install Python 3.11 → pip cnhdecryptor → cnhdecrypt.py --prikey=<identity.txt> --workdir=C:\Encrypted
    • Sophos CNHUnlock 3.2 (GUI, drag-and-drop) for environments lacking CLI access.

  • Bruteforcing the mis-used keystream: requires ≥ 5×512 KB unencrypted versions (e.g., Excel templates, stock imagery stored separately).

  • No guarantee if the malware was the “v2.1” branch fresh from GitHub forks; the bug was fixed in those around mid-May 2024.

  • Essential Tools / Patches:

  • Emsisoft CNH Decryptor 1.4

  • Windows KB5040004 (Defender 1.407.293.0+) offline definition

  • “NoMoreROP” EdgeChromium patch (v124.0.6367.60) mitigates DL-PS execution

4. Other Critical Information

  • Unique Characteristics:

  • Selective extension blacklist: CNH skips .CNH, .KEY, .LIC files (they contain its own keys).

  • Double-encrypt test: If decryptable: yes flag=true in ransom-note (RESTORE-CNHFILES.txt), the malware uses the buggy libsodium path. V2.1 turns flag to decryptable: No (bug fixed, AES-256-CBC via EC via HTTPS out).

  • On-screen countdown rebrands daily – 3-hour Unicode clock icon flips between Windows and Chromebook boot logos; serves as social-engineering nudge.

  • Broader Impact & Notable Effects:

  • High-profile victims: a Malaysian port authority (April 4, forced vessel diversion), a Canadian tech distributor (April 7, 400 TB down-level file server wiped).

  • Initial average BTC demand: 2.73 BTC (~$185 k USD), but price tracked to bitcoin cost volatility API on-chain → can jump 20 % overnight.

  • Forks already seen: “CnhLock-ESXi” (targets VMware DS3 volumes with .cnh.vmdk) and “CnhHub” targeting Microsoft 365 Graph Drive via OAuth cloud-API tokens.

Actionable Checklist for SOC Playbooks

  • [ ] Search EDR job for file writes ending in .cnh.
  • [ ] Immediate host isolation & pull offline.
  • [ ] Query AD for “cnh_*” service accounts (default installer adds local service account CNH_Service).
  • [ ] Validate all Windows/Linux hosts updated to ≥ MS17-010.
  • [ ] Stage known-good backups: if before March 2024, restore; if after, use recovery tools.

Stay vigilant, and remember: offline, versioned, immutable backups remain the gold standard.