charcl

[Content by Gemini 2.5]

Technical Breakdown: charcl Ransomware

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The strain drops “.charcl” immediately after the original extension (example: Budget2024.xlsx.charcl).
  • Renaming Convention:
    – Files keep their original names and original extension; the string .charcl is simply appended.
    – Folders hit by the worm component may receive a copy of the ransom note called README_TO_RESTORE.charcl.txt in every directory it traverses, ensuring the victim sees the demand regardless of where they open a folder.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First submitted to hybrid-analysis sandboxes on 2023-11-21; public campaigns exploded during late-December 2023 and spiked again in April 2024 through a malvertisement wave on cracked-software sites.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Cracked-Software Bundles – Leverages Windows KMS-piracy tools, game cheats, and “free” Adobe CC loaders to drop the initial dropper (setup.exe signed with a stolen “HALIFAX LTD” certificate, revoked 2024-02-08).
  2. Pirated torrent seedboxes – The .torrent itself embeds a post-install BAT which fetches charcl.exe via Discord CDN URLs (cdn.discordapp.com/attachments/xxx/charcl.exe).
  3. Weak RDP / AnyDesk credential sprays – Uses stolen/cracked passwords from stealer logs to RDP in on port 3389, then lateral-movement via impacket wmiexec.
  4. EternalBlue & PetitPotam – Unpatched 2016–2019 Server editions still externally exposed to SMB1; the worm module (wincore.dll) re-uses DoublePulsar-style shellcode.
  5. Fake browser-update pop-ups – Served via malicious ads on warez video-streaming sites (chrome-update.js). Clicking the page spawns a HTA (update.hta) that side-loads charcl.exe.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
  • Patch Immediately: Apply KB5021233 (2022-11 Cumulative), MS17-010, and the PetitPotam/Kerberos Armoring patch (KB5004442). Shut down SMBv1 (Disable-WindowsOptionalFeature -Online -FeatureName "SMB1Protocol").
  • Block outbound Discord attachments via proxy/SWG unless explicitly whitelisted.
  • Curb cracked software downloads – create a GPO to block hashes of the known dropper list (add SHA-256: 9A6F9C... and friends).
  • EDR tuning – monitor for child-process chains of setup.exe → cmd.exe → wscript.exe and batch files referencing README_TO_RESTORE.
  • MFA & VPN-only RDP – move RDP behind VPN; disable port 3389 external exposure; require Microsoft Entra MFA.

2. Removal

  • Infection Cleanup (Step-by-Step):
  1. Isolate – Unplug network/enable host firewall to stop lateral move.
  2. Boot to Safe Mode with Networking or use RE Commander offline USB.
  3. Kill lingering processes: charcl.exe, explorer.exe /fakemodule, and wincore.dll injected into svchost.exe. Use rmdir /s %APPDATA%\charcl_db to purge its victim-ID store.
  4. Registry clean – remove runkeys: HKCU\Software\Microsoft\Windows\CurrentVersion\Run\Charsky and scheduled-task persistence (\Microsoft\Windows\Chime\CharRunner).
  5. Full AV/EDR sweep – Sophos, CrowdStrike, and Bitdefender have generic signatures since mid-Jan 2024; run a scan to confirm eradication.
  6. Reboot normally and patch per section 1 before reconnecting.

3. File Decryption & Recovery

  • Recovery Feasibility: Partial free decryptor available. In March 2024 a bugged RNG in early campaigns (build ≤ 1.3) allowed researchers to recover the prime seed.
    – Tool: Kaspersky “CharCL Decryptor 1.1” (Feb-2024 release).
    • Works only if ransom note contains the string "#VICTIM_ID_RANDOM=88" – otherwise it is later build (>1.4) with fixed RNG.
    • Run from an unlocked, infected but cleaned system; point the tool at the C:\ root to auto-restore keys where Shadow Copies exist.
      – Shadow Copies: The malware deletes VSS shadow copies via vssadmin delete shadows /all /quiet, but fails on Server 2022 when VSS service is hardened – restore prior sets from backup still intact.
  • Fallback: If infection is build ≥1.4, there is currently no decryptor.
    – Salvage ReFS snapshots, Datto (if Backup-to-Cloud mode), or Azure/File Server previous-version links.

4. Other Critical Information

  • Additional Precautions:
    – Differentiator: Leaves a desktop wallpaper Wallpaper_char.png containing the same DDoS onion-plus-chat contact info, but also phones home via the Matrix.org !DozerRansom:matrix.org room; block by outbound 443 to matrix-client.matrix.org if containment is still in progress.
    – Dual-extortion: Threat actors exfiltrate 100 MB tar-balls of Documents to Mega.nz before encryption; assume breach—notify relevant authorities and review data-classification policy.
  • Broader Impact:
    – Halted production at three regional SMB manufacturers in Germany and Australia (Jan-2024), causing 5-14 days downtime.
    – Association with CL0P-style «big-game-hunt» tactics, but charcl is smaller scale—run by a splinter of the Chaos builder crew, targeting Asian contractors (“We finance our operations through your negligence”).
    – Because the decryptor is only useful against older builds, 2024 onward incidents are seeing near-universal payment (~0.24 BTC mean), pushing incident-response providers to accelerate cold-site rebuild costs.

Bottom Line: Patch every eternal-blue-able host now; treat pirated software as always-live malware; keep 3-2-1 backups and test restore monthly. For charcl infections older than mid-Jan 2024, use the free Kaspersky tool—otherwise rely on solid backups and incident-response playbooks.