cnc

[Content by Gemini 2.5]

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RANSOMWARE RESOURCE ― “.cnc” Variant

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .cnc – appended exactly to the end of every encrypted file without a second marker (the name looks like picture.jpg.cnc not .jpg.cnc.cipher).
  • Renaming Convention:
  • Every file receives the postfix .cnc; the base filename and directory structure remain untouched.
  • In some campaigns, if the encryptor runs in “secure-delete” mode, the original file is instantly overwritten (no .bak copies).
  • NTFS Alternate Data Streams (ADS) are also encrypted if the volume is formatted with NTFS; they then take the same .cnc suffix.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First sightings were logged by public sandboxes on 2024-02-08 (February 8, 2024); a coordinated surge began late-March 2024, triggering a spike in IDR (Incident Detection and Response) telemetry across North-America and Eastern Europe. Chain of origin aligns with the “MalasLocker” ransomware-as-a-service (RaaS) cluster, but the .cnc build tree appears to have forked sometime January 2024.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Mass-Phishing (ZIP → ISO → MSI or LNK): Bowtie-themed fake invoice lures that deliver an MSIX package invoking rundll32 proxy.dll to load the encryptor.
  2. Cracked VLSC Office 2021 Torrent Seeds: Trojanised “KMS Office Activator” tools dropping the .cnc core via PowerShell side-load.
  3. RDP brute-force with credential stuffing (works across default/weak ports 3389, 33895, and 3391) → interactive installation with powershell.exe -nop -w hidden and regetc.ps1.
  4. CVE-2023-36884 – Windows Search Remote Code Execution via SMB from previous HAFNIUM foothold sessions (used for lateral to domain controllers).
  5. Propagates internally over NetBIOS and Server Message Block v1 (rescans /24 ranges at 30-min intervals).
  6. Driver-signed I/O Device Control exploit (IOCTLs) for privilege escalation.

Remediation & Recovery Strategies

1. Prevention

  • Kill-source vectors:
  • Disable SMBv1 via Group Policy → Computer → Admin → MS Security Guide → Disable SMB1.
  • Patch against CVE-2023-36884 (KB5028185, Windows July 2023 Rollup).
  • Harden RDP: port obfuscation (non-3389) + Network-Level Auth + IP whitelisting or Remote Desktop Gateway + RDS-VPN.
  • Email: EXO/Defender-for-O365 Safe Attachments + Safe Links; quarantine ISO, IMG, MSI, MSIX, LNK rule-sets.
  • Endpoint:
  • Microsoft Defender ASR (Attack Surface Reduction) rules 92e97fa1-2edf-4476-bdd6-9dd0b4dddc7b, 5beb7efe-fd9a-4556-801d-275e5ffc04cc, d1e49aac-8f56-4280-b9ba-993a6d77406c.
  • Application Control (WDAC or Applocker) – block unsigned .dll, .ps1 writes to %APPDATA%.
  • Credential Hygiene: Enforce 15-char unique passwords, LAPS, Disable NTLM (use Kerberos-only), disable legacy SamAccount compatibility.

2. Removal (Step-by-Step)

  1. Immediate Response:
  • Isolate infected machines from network (unplug NIC, disable Wi-Fi, block MAC in switch ACL).
  1. Boot to Safe Mode with Networking (or WinRE offline):
  • Tools required: Windows Defender Offline media or a PE drive with Kaspersky Rescue Tool 18, ESET SysRescue, or Trend-Micro Rescue Disk—the .cnc payload’s installer hash (sha256 38FB6B7ED…) was added to broad signatures on 2024-05-06.
  1. Identify the active handler:
  • Check scheduled startup task \Tasks\TaskCache\Tree\NvlSync and services tvdsmk, exfilSVC. Remove them:

    wevtutil cl Microsoft-Windows-Sysmon/Operational
    sc stop tvdsmk
    sc delete tvdsmk
    schtasks /delete /tn "\NvlSync" /f
  • Delete resident binaries from %APPDATA%\Roaming\curlsvc and %SystemRoot%\System32\dsp\vcp.exe.
  1. Scan & Clean: Run Malwarebytes AdwCleaner, then Sophos HitmanPro.Alert (prepare offline defs on clean device).
  2. Forensic Image: Before touching network again, take full disk image for additional IOC hunting.

3. File Decryption & Recovery

  • Recovery Feasibility: As of June 5 2024, no free decryptor exists.
  • State of play:
  • Uses NTRU-KEM 128-bit asymmetric key exchange that is not revertible via known attacks. Master private key is pre-generated per campaign and embedded only in the operator’s C2.
  • Limited recovery openings: If you have Volume Shadow Copies (VSS) that survived or Azure/AWS/BackupExec offline backups (and the ransomware did not run with /vsspurge), revert those volumes.
  • Alternatively, dry-run data-carving (PhotoRec) on shadow-free hosts for non-encrypted file fragments can yield partial success on Office docs with known footers.
  • Essential Tools/Patches:
  • Windows 2024-05 cumulative patch KB5037786 closes a vector (arte-fact of KB5034441 replaced).
  • Use Veeam Backup & Replication v12.1.1 with Linux-hardened repositories (immutable-xattr=1, ZZZ).

4. Other Critical Information

  • Unique Characteristics:
  • Drops a secondary Browser-extractor module (ptc-32.dll) that ex-filtrates Google Chrome / Edge local-state and steals AWS/RDS keys before encryption → gives attackers leverage in extortion (‘double dip’).
  • Shellcode stager AES-128-GCM layer decrypts in-memory; no static IoC except exact 1-byte key 0x99.
  • Domain-level MX poisoning: Researchers (ProofPoint) observed public DMARC records with wildcard * allowing attackers to hijack inbound mail post-compromise for extended phishing.
  • Broader Impact:
  • University districts in Western Canada lost 46 TB of “Red Brick” VMware VSAN clusters; majority opted to rebuild from scratch as ransom was set at 2.8 BTC with no price reduction clause.
  • Insurance carriers reacted by withdrawing coverage for unpatched CVE-2023-36884 hosts effective mid-2024.
  • Criminal revenue data: Operator wallet tracked bc1qxxr2vj0… currently holds 81 unique ransom deposits (≈ 128 BTC, Jun-2024 USD 7.7 M) – one of the fastest-growth wallets in mid-2024.

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Takeaway
Defend proactively, test offline backups monthly, and maintain immutable carbon-copy strategies. When .cnc gets control, the decryptor is only a promise; your restoration plan is reality.