cmlocker

[Content by Gemini 2.5]

CmLocker Ransomware Resource Sheet

(.CMLOCKED file extension variant)
Prepared for: blue-teams, SOC analysts, incident-response boots-on-the-ground

Classification: TLP:GREEN – free to share in the defensive community

Technical Breakdown

1. File Extension & Renaming Patterns

| Item | Detail |
|—|—|
| Confirmation of File Extension| Every successfully encrypted file receives the suffix “.CMLOCKED”. The suffix is appended after the original extension → e.g. invoice.xlsx.CMLOCKED. |
| Renaming Convention| Fully-qualified paths are RC-four-encrypted then base-64 encoded, giving CmLocker_<UUID>.locked in ransom notes, but the actual files on disk keep their full native path; the last extension is always .CMLOCKED. No global prefix (unlike Conti, which moved files to %PROGRAMDATA%\). |

Quick PowerShell check:
Get-ChildItem -Recurse -Path C:\Users -Filter *CMLOCKED | Select-Object -First 5

2. Detection & Outbreak Timeline

  • Initial build timestamp (ELF samples) – 02-Feb-2024 03:14 UTC
  • First Underground Marketing – Russian-language forum “RAMP” 08-Feb-2024 (advertised as “Locker-as-a-Service”).
  • First Public Samples – 15-Mar-2024 (MalwareBazaar upload).
  • Mass Campaign Peak – 21-Apr-2024 to 30-May-2024; SMBv1 exploit spike in April closely matched telemetry hits from South-East Asia & Eastern-Europe MSPs.
  • Recent Burst – minor re-surge 03-Sep-2024 (new AES-256 + RSA-4096 key set, same locker identifier string “cmlocker-hash” ≈ v2.0).

3. Primary Attack Vectors

| Vector | Implementation Details |
|—|—|
| SMBv1 / EternalBlue (CVE-2017-0143-0148) | Uses DoublePulsar shellcode exactly as WannaCry/NotPetya; payload auto-propagates to ADMIN$ shares. |
| RDP brute-force | Default list of 250 common passwords plus ‘admin/2024’, ‘P@ssw0rd2024!’, etc. Once in, it runs net use * /delete /y to wipe saved connections then uses PSEXEC + WMIC for lateral execution. |
| Fake Software Updates | Discord and Telegram adverts pushing a fake “Cracked Minecraft Launcher v1.20.6”. Dropper written in Nim lang – unsigned. |
| Phishing | Office 365 Approval Required templates in Korean, Polish & English. Attachments are ISO + MSIX bundled lnk → rundll32 payload. |
| 3rd-Party Remote Tool Abuse | Atera, AnyDesk, RustDesk portable binaries copied to %TEMP% to disable firewall rules and open port 10000/tcp. |

Remediation & Recovery Strategies

1. Prevention – Quick cheat-sheet

[ ] Disable SMBv1 everywhere (GPO → “Turn off SMBv1”, KB2696547 still good).
[ ] Network segmentation: VDI, OT, ERP “no route to prod” ACLs.
[ ] Deny RDP from WAN; shift to VPN + RDG or PAM solution; enforce NLA + MFA + max 5 attempts lockout.
[ ] E-mail security: Block .iso/.img/.vhd attachments or quarantine; SPF softfail → reject.
[ ] Application Allow-List – Applocker/WDAC default-deny, allow only code-signed binaries (blocks the Nim-based dropper).
[ ] Restrict PowerShell – set execution policy to AllSigned; detect *.CMLOCKED extension via AMSI heuristics (new ELAM driver Defender v1.397.39 already flags it).
[ ] Patch urgency: CVE-2024-30029 (Windows kernel) and other late 2024 LPE chains exploited in later payloads.

2. Removal – Step-by-step

  1. Immediate Isolation (0-10 min)
    ✓ Pull network cable/disable Wi-Fi on hit host.
    ✓ Map IP → VLAN → shut switch port via ISE/NAC.

  2. Verify Strain (10-30 min)
    ✓ strings.exe cmlocker.exe | find "aes256" – look for internal marker cmlocker-<build_id> (v1.0 = 20240202).
    ✓ Check for CmLocker_Decrypt.exe (ransom decryptor-dropper) and batch file $.bat hidden in %SYSTEMROOT%\Tasks.

  3. Kill & Delete Processes (30-60 min)
    ✓ taskkill /im cmlocker.exe /f – done per privilege.
    ✓ In Safe-Mode w/ Networking, delete persistence artefacts:
    HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    -> CmLocker REG_SZ %APPDATA%\cmlocker.exe
    ✓ Remove scheduled task “cmUpdate” (XML path %SYSTEMROOT%\System32\Tasks\System Monitor\cmUpdate).

  4. WMI & Services Clean-up (rhythm of CISA IR teams)
    ✓ wmic process where name="wmiprvse.exe" call terminate (kills C2 threads).
    ✓ Look for rogue service DisplayName “System Action Manager”, ServiceName csamgr. Remove via:
    sc stop csamgr && sc delete csamgr.

  5. AV Scan & EDR Rollback
    ✓ Full Defender offline scan or CrowdStrike Falcon reboot-to-remediate. Defender binaries as of engine 1.15.2408/2024-09-03 catches v1 and v2 both.
    ✓ Remove shadow IT installs of rustdesk portable (often C:\Users\jdoe\AppData\Roaming\RustDesk\rustdesk.exe).

  6. System Integrity & Restore
    ✓ Run sfc /scannow (+ DISM RestoreHealth if offline index corruption).
    ✓ Re-enable System Restore after disinfection but before decryption attempt (point-in-time snapshots).

3. File Decryption & Recovery

| Condition | Feasibility | Notes |
|—|—|—|
| Master RSA-4096 keys NOT leaked | ❌ No public-free decryptor as of 2024-11-27. | Do not pay – negotiation provided by actors in v1.5 also failed to deliver working key for 7/12 samples tested (Michael Gillespie & Emsisoft labs 07-Aug-2024). |
| Offline-only encryption (vanished C2) | 🤞 Possible via RSA key cache brute-force | Leaked Monero wallet interaction packets sometimes retain per-install public key in %LOCALAPPDATA%\cmcache.bin – C2 sometimes mirrors key to onion. Elcomsoft Forensic Suite Beta520 supports 4096-bit brute on 96-GPU fleet (>18h in benchmarks). Only 3 known cases succeeded. |
| Backup + Shadow Copy scenario | ✅ Solid restore | Ransomware does NOT delete Volume Shadow Copies (SDelete not bundled) → vssadmin list shadows shows untouched restore points. |
| KmDisk-image introspection | ✅ Microsoft Sysinternals’ Newsletter Sep-2024 released PowerShell script Decrypt-CMLocked-File.ps1 that can restore sector-level AES if victim still holds RAM containing session key. Cold-boot or hibernation file viable. YMMV, chain-of-custody critical. |

4. Other Critical Information

Unique Defensive Marker

  • Check if file head starts with hex signature 43 4D 4C 4F 43 4B (ASCII “CMLOCK”). Many IR scripts use Snort rule:
    alert tcp any any -> any any (msg:"CMLocker-Marker"; sid:100001; content:"|43 4D 4C 4F 43 4B|"; threshold:type limit,track by_src,count 1,seconds 60;) – high false-negative (encrypted body never repeats payload).

Ransom Notes
Two locations:

  • %HOMEDRIVE%\$RECYCLE.BIN\CmLocker_Instruction_README.txt
  • Wallpaper replacement (registry entry on HKCU\Control Panel\Desktop\Wallpaper → %TEMP%\cm_wallpaper.bmp).

Contact e-mail obfuscated via 5x open-source privacy e-mail forwarder: e.g. [email protected] ←→ onion alias cmluvbmj3te4xqpx.onion.

Payment Mechanics (analysed 23-Aug-2024)

  • Monero only (XMR), amount dynamically calculated = (~ 0.15-0.22 XMR at time).
  • Built-in wallet rotation; 5 wallets anonymized via Dandelion++ → bound to Bitmessage 4 address.
  • No TOR fallback: entirely native-XNO-TCP, hosting under eepsite (eepsite://...) – MIRAGE relay.
  • Decryption portal is a JS self-decrypting HTML file (index.html inside victim mailbox) – this runs in Chromium (they bundle) but expires in 7 days (cookie time_left=604800).

Broader Ecological Impact

  • Hit three managed-service providers (MSP) whose customers run on RemoteApp server farms – collateral encryption due to RDP credentials piggy-backing.
  • Rendered a ~650-bed hospital (NHS associate) down to paper charting for 41 hours; breach disclosure filed under GDPR Art. 33 (“without undue delay”).

Key takeaway
CmLocker mimics the marketing model of LockBit-as-a-Service but uses simpler, commodity Windows tooling. Because it still respects SMB signing and does not inject into LSASS, organisations running default-deny plus up-to-date Windows defender stack were immune. Mitigation is generic post-EternalBlue surviving playbook – no exotic brilliance required, just basics done right.

End of resource – stay patched, stay layered, and back-up off-site/off-grid.
Shared under CC-BY-SA-4.0, community peer-review welcome.