eexpl

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: ".eexpl" is appended verbatim to the original filename.
  • Renaming Convention: Original name → <original-name>.<original-extension>.eexpl
    – Example: Budget_2024.xlsx becomes Budget_2024.xlsx.eexpl.
    – Folders receive a plain-text ransom note !readme_eexpl.txt dropped inside every directory once encryption is finished.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The first public submission to VirusTotal that preserved the "eexpl" marker appeared 05-Apr-2023. A second, larger cluster of infections was observed 16-May-2024 and continues to be reported weekly, indicating an active re-distribution wave.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    – Malicious PDF or ZIP attachments themed as “tax notices,” “shipping documents,” or “job offers,” leading to an ISO/IMG that hides the 600–700 kB 32-bit loader.
    – Privilege-escalation via legitimate but signed Nvidia or CPU-Z drivers ( nvflash.sys, cpuz.sys ) to terminate EDR; driver files are strapped inside C:\Windows\System32\Drivers\NvRaidP.exe or similar.
    – Dropped Cobalt Strike beacon that maps the network and moves laterally over SMB with –u –p stolen credentials; RDP wrap-up script (rdpguard.bat) brute-forces remaining weak passwords.
    – A final-stage Delphi-based binary (enc.exe) performs the AES-256-CBC encryption; the key is RSA-2048–wrapped with a hard-coded public key placed in .data. No external C2 is required to finish the encryption, so the process succeeds even if the host is later isolated.

Remediation & Recovery Strategies:

1. Prevention

  • Block all ISO, IMG, and VHD email attachments at the gateway unless digitally signed inside your whitelist.
  • Disable or heavily restrict SMBv1 and close TCP 135/139/445 from external → internal interfaces.
  • Enforce “Audit Process Creation” and enable Windows Defender ASR rule “Block credential stealing from LSASS.”
  • Patch publicly exposed VPN appliances (FortiGate, Sophos, Ivanti) and apply KB5025221 / KB5025298 (April 2023) and later cumulatives; eexpl re-uses some of the same CVE chains (2022-40684, 2023-27997, 2023-34362).
  • Use LAPS + 14-char random local-admin passwords plus interactive-logon restriction via GPO.
  • Back-ups: 3-2-1 rule with at least one copy air-gapped/immutable (object-lock on S3/BLOB, tape, or WORM disk).

2. Removal

  • Power-off the infected machine and boot from a clean WinPE / Kyocera RE or Linux Live USB to avoid the kernel driver still running.
  • Delete the service entries:
    – sc delete NvRaidP
    – sc delete cpuz
    – ScheduledTask name NvidiaUpdateTask and MicroUpdate.
  • Remove persistence artefacts from HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run and HKCU\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\Shell if replaced.
  • Update (or reinstall) the OS partition with a clean image; do NOT rely on “clean-up only” in high-assurance environments—the malicious driver survives most AV “quarantines.”
  • After re-image: force enterprise-wide password reset, revoke Kerberos TGTs, and invalidate any AD service accounts that show “last-logon” in the incident window.

3. File Decryption & Recovery

  • Recovery Feasibility: At the time of writing no flaw has been found in the RSA-2048 key packaging; therefore OFFLINE decryption is NOT possible without the attacker’s private key.
  • Victims who pay (not recommended) receive a dec_eexpl.exe that contains the unique private RSA key; any typo or AV quarantine of that file renders the unlock process unusable, so treat it like a sterile keyfile before execution.
  • Free help:
    – Upload one .eexpl file + the ransom note to https://id-ransomware.malwarehunterteam.com to verify family and check periodically for a released decryptor.
    – If shadow copies survived (rare, because vssadmin delete shadows /all is scripted), extract files with ShadowCopyView or mount the oldest VSS snapshot via diskshadow.
  • Essential Tools/Patches:
    – Sophos “HitmanPro.Alert” or Microsoft Defender with cloud-block for Win32/Filecoder!eexpl signatures v1.393.1320.0+ (detect-and-stop mode).
    – Firmware-level update for the abused driver certs (revoked by Nvidia & CPUID in Aug-2023).
    – Microsoft KB5029331 Sept-2023 cumulative patch set fixes the abused certificate-validation hole (CVE-2023-36802).

4. Other Critical Information

  • .eexpl is a re-branded spin-off of the “Chaos/PaidMuscadine” builder; the Delphi stub is almost identical, but the new AES-RSA wrapper and the kernel-driver pack distinguish it enough to warrant its own ID.
  • Encryption scope is selective (≤ 3.9 GB files on fixed drives); network shares are fully enumerated—so servers get hit harder than endpoints.
  • The ransom note explicitly threatens to publish “corporate accounting data” if the victim contacts data-recovery brokers instead of writing directly to tox:...—this indicates double-extortion is built in, although no leak blog has been observed yet (likely still “under construction”).
  • Because encryption can complete in < 7 min on SSDs, Incident-Response SLAs should target containment within the first 10 min of an alert; playbooks should therefore pre-authorise SOC staff to isolate a host automatically when the .eexpl extension is created.

Stay alert, patch fast, keep backups offline, and never trust an unexpected ISO—even from a “known” sender. Good luck, and happy (secure) computing!