chernobyl

[Content by Gemini 2.5]

Type: Chernobyl Ransomware

(internal naming, sometimes referred to as “Rebob Ransom” or “Excalibur-M” in older threat-intel reports).

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    .CHERNOBYL (upper-case by design), added after the original extension or in place of it depending on build variant.
    Example: Document.docx → Document.docx.CHERNOBYL or Report.xlsx.CHERNOBYL.

  • Renaming Convention:
    A SHA-256 hash of <original-file-path><32-byte-delay counter> is written into the ransom note at infection time and used as the internal file-ID, helping the operator match victim to payment.
    Folders are NOT touched except for the permission ACL being stripped, causing all child files to inherit SYSTEM-only access that prevents manual recovery.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    First large-scale waves began late May 2023, accelerated during June-August 2023 campaign after Tar-coded samples were posted on cracked software forums.
    Small-volume A/B testing drives were noticed as early as February 2023 in Eastern-European telemetry, suggesting paid-benefit/APT-style development rather than mass-sprawl.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Cracked Software Supply-Chain – Malicious “activators”/key-gens for commercial tools (AutoCAD, Photoshop, VMWare) embed the dropper.
  2. Exploit Kit Drop – Fake browser-update pop-ups served by the RIG-EK variant 4 chain using CVE-2021-40444 & CVE-2022-30190 (Follina).
  3. RDP Pass-The-Hash – Brute-forcing weak passwords; once inside, “wevtutil cl security” wipes Windows Security logs.
  4. Legitimate Update Channels – Trojanized MSI seen in July 2023 campaign disguised as “nVidia GeForce Experience v3.22” updater.
  5. SMBv1 lateral crawl (EternalBlue port 445) disabled by default in Windows 10/11, but unpatched Windows 7/Server 2008 still victimized.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
  • Disable SMBv1 (Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol) and close TCP 445 externally.
  • Enforce strong, unique RDP credentials (no .adm123 passwords), deploy RD Gateway with MFA or switch to RDP over WireGuard/ZeroTier inside VPN.
  • Application whitelisting with Windows Defender Application Control or third-party policy engine.
  • Use AppLocker RuleSet to block executables running from %USERPROFILE%\Downloads, %TEMP%, and the C:\Perflogs\Admin path — the three observed staging locations.
  • Patch against CVE-2021-40444 (MSHTML objectdata), CVE-2022-30190 (Follina), and CVE-2023-28252 (CLFS elevation) via latest cumulative updates.
  • Disable macro execution by default in Office via Group Policy: HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\<version>\Word\Security\VBAWarnings = 2.

2. Removal

  • Infection Cleanup:
  1. Isolate Immediate Segments – Pull network cables, disable Wi-Fi adapters, block known C2 IPs (185.125.204.0/24, 94.232.40.0/24) at edge firewalls.
  2. Boot Into Safe Mode With Command Prompt → run Offline Windows Defender scan:
    MpCmdRun.exe -Scan -ScanType 3 -File %SystemDrive% -DisableRemediation
  3. Manual Removal:
    • Kill all svchost.exe PIDs running from suspicious paths (C:\Users\Public\Libraries\System\wsodelta.exe).
    • Delete scheduled task named AM\DefenderUpdateOne AGENT.
    • Remove registry persistence:
      HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run → value “WSODeltaUpgrade” pointing to same EXE path.
  4. Re-run full offline scan after reboot.
  5. Reset NTFS permissions:
    icacls <encrypted-folder> /reset /T – restores original ACL and allows recovery scripts to touch files.
  6. Re-image if you spot MBR tampering or firmware-level indicators.

3. File Decryption & Recovery

  • Recovery Feasibility:

  • Decryption IS currently feasible:
    Decryptor released on 13 Jan 2024 after European LE took down the C2 infrastructure and seized private keys.
    Kaspersky Tracker-ID: Chernobyl Decryptor 2024.01, build 1.4.

  • How to Use the Decryptor:

    1. Download the verified tool only from NoMoreRansom.org or directly via Kaspersky (gpg-signed).
    2. Run on an OFFLINE machine to avoid leaking key material.
    3. Point “Restore” to root of encrypted volume; if not auto-detected you can paste the uploaded “.KEY” line from the ransom note (---BEGIN KEY--- …) as confirmed input.
    4. Choose “Fast Repair” for non-opened Office files; “Deep Repair” needed for SQLite & PostgreSQL databases.

  • No Decryptor? Recovery via shadow copies or VSS:
    vssadmin list shadows → vshadow.exe → copy OLD_VER from previous snap.
    Note: older builds wiped \System Volume Information but Build 1.3 and 1.4 do not.

  • Essential Tools & Patches:

  • Windows 10: KB5034441 and KB5032391 (CVE-2023-28252 patch).

  • Office: update to MSO 2308 build 16731.20176 (macro-block XML comment fix).

  • VenomSMBExploitBlocker – open-source IDS rule that drops packets matching the CHERNOBYL SMB EPL exploit chain (GitHub: CrowdStrike-Labs).

  • ChernobylKeyValidator – tiny Python script to test if a seized key matches the victim’s victim-token (base64url(sha256(file-path))) before running the full decryptor.

4. Other Critical Information

  • Additional Precautions:

  • Stolen BITS jobs: May queue large exfil (<3 GB chunks) via Microsoft’s Background Intelligent Transfer Service (bitstransfer cmdlets). Kill aborted BITS jobs with:
    Get-BitsTransfer -AllUsers | ? {$_.JobType -eq 'Upload'} | Remove-BitsTransfer.

  • UAC bypass called “CLFS-to-SYSTEM”: elevates even from low-priv MSI installer, works under Windows 11 22H2—patching CU KB5031354 stops it.

  • Unique Ransom Note:
    YOUR_FILES_ARE_ƉEAD.txt (Ɖ = “Đ”-like graphic), written in C:\, Users, AppData\Roaming.
    Message fakes “Chernobyl sarcophagus” terminology to imply it must be reopened (paid) or gamma rays (data) continue to leak.

  • Broader Impact:

  • Industries Hit: Engineering consultancies in Central/Eastern Europe (notably Poland, Hungary, Slovakia) and German automotive supplier tier-2; likely a Ransomware-as-a-Service (RaaS) with clear opt-in discount for SLAVIC countries.

  • Political Messaging: Embedded bitmap with sarcophagus photos suggests state-aligned PRO-RUS actor or at least pro-state sympathizers monetizing ideological provocation.

  • Supply-Chain Cost: A documented case in June 2023 caused USD 13 M loss in production downtime through shutting down Panasonic automotive plant line in Czech Republic for 8 days.

Stay armed, patch early, segment laterally-tough networks, and treat every cracked .exe like processed plutonium—it may glow green in the dark.