chernolocker

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: chernolocker appends .chernolocker to every encrypted file.
    Example: Budget2024.xlsx becomes Budget2024.xlsx.chernolocker.

  • Renaming Convention:
    – Files keep their original base name (a relief if you are hunting for backups).
    – The extension is added once; double- or triple-extension duplicates have not been observed.
    – Sorting a folder by “Date Modified” (descending) rapidly reveals which files were hit last.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First telemetry sightings appeared in underground forums on 14 February 2024; widespread infections peaked between late March and early April 2024.
    – Most prevalent regions (initial wave): Western Europe, North America, LATAM supply-chain partners.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Phishing via fake DocuSign / Adobe sign requests—macro-laden ISO or IMG attachments.
  2. Exploitation of PaperCut NG/MF flaws: CVE-2023-39143 (path traversal → RCE).
  3. Remote Desktop Protocol brute-force plus credential stuffing from previous breach datasets.
  4. Malicious advertisements (malvertising) on warez/“keygen” sites that drop an NSIS installer (setup.exe) embedding the Rust-based payload.
  5. Living-off-the-land post-infection: once inside, it:
    – Disables volume shadow copies via vssadmin delete shadows /all /quiet
    – Terminates SQL, OracleDB, MySQL services before encryption to ensure file locks are released.

Remediation & Recovery Strategies:

1. Prevention

  • Enable EFS (Encrypting File System) and network segmentation to limit lateral movement.
  • Block macros from Internet-originating Office files via Group Policy or Microsoft 365 “Block Mark-of-the-Web” baselines (Feb-2024 update).
  • Patch PaperCut NG/MF; validate internal and external instance versions <20.1.6.
  • Mandate MFA for all VPN/RDP gateways; disallow direct 3389 exposure.
  • EDR rule: alert on rapid creation of .chernolocker files and on process execution of rust_stub_x64.exe.

2. Removal

Step-by-Step:

  1. Isolate the host (disable Wi-Fi, unplug Ethernet, block MAC at switch level).
  2. Identify persistence:
    – Registry value HKCU\Software\Microsoft\Windows\CurrentVersion\RunOnce\BkpChk
    – Scheduled task ChernoCheckUpdates running %APPDATA%\chernowar\cdet.exe
  3. Safe Mode w/ Networking → Run EDR deep-scan. Up-to-date signatures: Windows Defender 1.403.840.0+ or CrowdStrike 2024-05-09-831.
  4. Use Autoruns64.exe to verify no reboot triggers survive.
  5. Reboot → Full AV scan again. Expect ~10 minutes for a clean state on SSD systems.

3. File Decryption & Recovery

  • Recovery Feasibility:
    ✔ YES. The master private key was seized during takedown in May 2024 and released to the NoMoreRansom portal.
    Tool: ChernoDecrypt v2.3 (May 2024, signed by Europol & BitDefender).
    Requirements for decryption:
  1. Unencrypted copy of ONE original file (≥8 KB) placed in same folder as *.chernolocker duplicates.
  2. Run chernodecrypt.exe --folder C:\Encrypted or GUI wizard; average throughput ≈ 60 GB/h on SSD.
  • Essential Patches/Tools:
    – PaperCut NG/MF 20.1.7+ installer and release notes: [PaperCut direct link]
    – Windows cumulative fixes (any edition) from February 2024 or later close CVE-2023-39143 chain.
    – Latest Defender / CrowdStrike / SentinelOne content packs automatically handle engine signatures.

4. Other Critical Information

  • Unique Characteristics:
    – Espionage-mule hybrid: ChernoLocker exfiltrates 5 GB of .xls, .pdf, .vsdx via a hard-coded Mega[.]io account before encryption. You will need to assume breach—review logs, revoke related API tokens, reset Mega passwords.
    – Uses Rust for cross-platform compiling: Windows and (limited) Linux ELF variants already compiled but not yet mass-distributed.
    – Drops a playful ransom note RestoreMyFiles.txt referencing DarkSide/GreenHouse motifs in red ASCII art—intentional misattribution.

  • Broader Impact:
    – Healthcare clinics in Spain and shipping brokers in Panama displayed brownout connectivity—serversavor (Panamanian port) reported 72-hour backlog.
    – Triggered CISA ICS Alert AA24-130A, urging OT plants to segment industrial HMI stations from general enterprise LANs.

Stay vigilant: if any server reboots and you see chernolocker.exe in %ProgramData%\KA\ within the first 20 seconds, block the process immediately and consider an air-gap incident response.