eeyu

[Content by Gemini 2.5]

Resource Sheet: The “.eeyu” Ransomware Variant

(STOP/Djvu family, observed early-May 2024)

PART 1 – TECHNICAL BREAKDOWN

  1. File Extension & Renaming Pattern
  • Extension added: .eeyu (lower-case, four characters, preceded by a dot).
  • Renaming convention: Original name is preserved, the extension is simply appended.
    Example: Project.xlsx → Project.xlsx.eeyu
  • Dropped marker file: _readme.txt (identical text placed in every folder, desktop, and %USERPROFILE%).
  1. Detection & Outbreak Timeline
  • First public submissions: 03-May-2024 on ID-Ransomware & VirusTotal.
  • Rapid distribution spike: 06-08-May-2024 (multiple campaigns hit YouTube-comment spam, “cracked” software sites and Keygen blogspots).
  • Current status: Active – new victims reported daily (particularly in Western Europe, LATAM, South-East Asia).
  1. Primary Attack Vectors
  • Pirated-software bundles (most common): fake Adobe, Ableton, AutoCAD, Windows activators, game mods.
  • SmokeLoader back-door delivered through the same bundle; once present, downloads eeyu payload and Cobalt Strike beacons.
  • Malvertising chain “FakeCAPTCHA” → fake codec update → MSI installer containing eeyu.
  • No self-spreading (worm) component – relies on user execution; therefore RDP / SMB-EternalBlue NOT used by standard builds (differentiate from Conti/Lapsus lateral-tooling).
  • UAC bypasses: fodhelper.exe & CMSTP proxies, followed by vssadmin delete shadows /all and bcdedit /set {default} recoveryenabled No.

PART 2 – REMEDIATION & RECOVERY

  1. Prevention (Immediate)
  • Block inbound/SMBv1 at perimeter (general hygiene) but note eeyu does not self-spread.
  • Restrict user write/execute rights to %AppData%, %Temp% (GPO Software Restriction Policies, Applocker).
  • Keep Windows & 3rd-party software fully patched (the malware itself arrives as user-land EXE yet secondary payloads exploit older flaws).
  • Disable Office macros by GPO; use Microsoft “Protected View” force-enable.
  • Maintain offline, versioned backups (3-2-1 rule) – STOP variants only target locally mapped drives, not object-storage buckets disconnected via S3 API.
  • Application whitelisting to stop payloads signed with invalid or stolen certificates (eeyu binaries commonly signed “OOO Favorit” or “ALEXANDR IVANOV”).
  • Install reputable AV with real-time behavioural shield; definitions added “Trojan:Win32/StopCrypt.S!ml” since early May 2024.

  1. Removal / Containment

  2. Disconnect NIC / disable Wi-Fi (stop exfiltration & further encryption).

  3. Power-on an unaffected admin account → disable questionable scheduled tasks (“Time Trigger Task”, “WindowsServices”, “SysHelper”).

  4. Boot into Safe Mode + Networking.

  5. Delete these artefacts:

    • %AppData%\LocalLow\{random}\build.exe
    • %Temp%\uu1.exe, uu2.exe (downloaders)
    • %ProgramData%\hibsys\hidemy.dll

  6. Run full scan with updated AV; follow with portable on-demand scanner (ESET Online, Malwarebytes, Kaspersky Virus Removal Tool) to catch SmokeLoader remnants.

  7. Clear all Shadow copies already deleted by malware but check Windows Backup & 3rd-party (Veeam, Acronis) catalogs.

  8. Change all local & cached domain passwords after clean-up – back-door routinely dumps LSASS.

  9. File Decryption & Recovery

  • Official decryptor: sometimes possible with the Emsisoft STOP-Djvu decryptor (v1.0.0.9 – May 2024).
    – Works ONLY if files were encrypted with an OFFLINE key (malware failed to reach its C2 and fell back to a hard-coded key).
    – Test: drag one pair of clean/encrypted files <1 MB into the tool; it will state “unknown online ID – decryption impossible” or “offline key – attempting”.
  • No free private-key leak at the time of writing; ransom demand $499 → $999 if not paid in 72 h. Payment leaves victims with mixed results (some receive working keys, others are ghosted).
  • ShadowExplorer, Recuva, PhotoRec – partial file rescue because ransomware spawns cipher /W to wipe free space; success limited to systems where process was interrupted.
  • Windows File-History & “Previous Versions” – usually purged (vssadmin delete shadows), but external USB drives disconnected at encryption-time may still contain intact snapshots.
  • Restore from backups (cloud object-versioning or offline disks) remains the most reliable vector.
  1. Other Critical Information
  • Family traits:
    – Uses Salsa20 + RSA-2040 (master key embedded inside .exe).
    – Drops identical ransom note (_readme.txt) with TOX ID and two mail addresses ([email protected], [email protected]).
    – Bizarre campaign grammar (“Don’t worry, you can return all your files!” + video-link “we can decrypt!” hosted on youtub●.com/watch?v=dQw4w…).
  • Extensions seen in same wave: .eeyu, .eucy, .wwah, .wwza – all STOP/Djvu fork, same decryptor applies.
  • Added persistence: registry RUN key HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run\SysHelper points to a copy in %ProgramData%.
  • Data exfiltration: minimal (only system info + campaign ID). No evidence of mass document stealing, but Cobalt Strike beacons may be used later for info-theft; assume compromise and rotate credentials.
  • Wider impact:
    – Home-users downloading “cracks” represent ~70 % of submissions; remainder are small businesses with poor patch/piracy hygiene.
    – Because this branch lacks lateral movement, enterprise domain-wide encryption is rare unless an admin executes the payload – still, single-share servers are routinely hit via mapped drives.
    – The constant churn of new extensions (roughly two per week) allows the affiliate programme to stay ahead of plain-extension-blocking rules; behaviour-based detection is therefore essential.

QUICK-SUMMARY CHEATSHEET

  • Extension = .eeyu → STOP/Djvu strain, May-2024 wave.
  • Infection vector: pirated software or fake codec, not wormable.
  • Isolate → delete artefacts → run AV → try Emsisoft STOP-decryptor with “offline” key → fall back to clean backups.
  • Prevention: stop piracy habit, disable macros, patch, 3-2-1 backups, Applocker.
  • Do NOT pay unless no backup and decryptor fails; success rate <60 % and fuels crime-ware economy.

Stay vigilant, keep those offline backups disconnected, and share IoCs with your local CERT. Good luck – the community defeats ransomware one refusal-to-pay at a time.