eemv

[Content by Gemini 2.5]

Ransomware Brief – “.eemv“ variant (DJVU/STOP family)

TECHNICAL BREAKDOWN

1. File extension & renaming patterns

  • Extension appended: .eemv (lower-case, four letters, no space or bracket)
  • Renaming convention:
    OriginalName.jpg → OriginalName.jpg.eemv
    The file name itself is NOT scrambled—only the extension is added.
    A text note is dropped in every folder + the desktop: _readme.txt

2. Detection & outbreak timeline

  • First public submissions: 07-Feb-2024 (ID-Ransomware, VirusTotal)
  • Peak distribution window: 07-Feb-2024 → 20-Feb-2024 (multiple waves)
  • Still circulating through the usual DJVU affiliate channels (fake cracks, adware bundles, RedLine info-stealer follow-on drops).

3. Primary attack vectors

DJVU is entirely Windows-centric and “affiliate driven”; .eemv samples caught in the wild were delivered by:

  1. Software-installer impersonation – Adobe Photoshop, Windows 11 activator, game cheat posted on YouTube + BitTorrent.
  2. Adware bundle installers (via “mstqd0” loader) that disable Defender through C:\Users\%username%\AppData\Local\Temp\2c9f.bat.
  3. RedLine or Vidar info-stealer pre-infection – credentials harvested, then .eemv dropped a few hours later.
  4. No sign of manual RDP or big SMB exploit chain for this wave (unlike Ryuki, Phobos, etc.).

REMEDIATION & RECOVERY STRATEGIES

1. Prevention

  • Defender updates: Ensure Microsoft Defender (or any AV with cloud protection) is ON – signatures detect Ransom:Win32/Stop.PAG since 1.403.118.0 (8-Feb-2024).
  • Application control: Turn on ASR rule “Block executable files from running unless they meet a prevalence, age, or trusted list criterion” (GUID d1e49aac-80ff-4ec4-a6c6-6224dee9af9e).
  • Disable Office macros from the Internet and disable MSIX/APPX sideloading if not needed—current DJVU often masquerades as .MSI.
  • Patch: No specific CVE for DJVU, but keep OS fully patched; old SMB or BlueKeep bugs are sometimes chained in later-stage movement.
  • Network segmentation & LAPS – prevents credential-theft pivot that usually precedes ransomware.

2. Removal / Infection clean-up

  1. Physically isolate the machine; pull Ethernet / disable Wi-Fi.
  2. Boot into Safe Mode with Networking.
  3. Use a clean media PC to download current portable scanner (Defender offline, ESET Online, Malwarebytes 5.x).
    – Stop processes:
    c:\users\public\build.exe, c:\users\public\encrypted.exe (random names, always unsigned).
    – Remove scheduled task Time Trigger Task or SystemSounds (runs the EXE on log-on).
  4. Clean restore-points: vssadmin delete shadows /all executed by the malware—do NOT rely on local shadow copies.
  5. Check registry autoruns:
    HKCU\Software\Microsoft\Windows\CurrentVersion\Run\\“gwx” = “C:\Users\Public\build.exe” (value name differs).
  6. Reboot → full scan second pass → only when system is clean and offline proceed to file-recovery efforts.

3. File decryption & recovery

  • DJVU / STOP uses OFFLINE & ONLINE keys.
    – OFFLINE (when the malware cannot reach its command server): decryptable with Emsisoft’s STOP(djvu)-decrypter (v1.0.0.7 updated 15-Feb-2024).
    – ONLINE (unique key per victim): decryptor cannot calculate the private key; no flaw in the cryptography (RSA-2048 + Salsa20).
  • How to check which key you have: open C:\SystemID\PersonalID.txt or any C:\ID-[random].txt.
    A fixed 64-char offline ID ending in t1 means the universal offline key exists = you can decrypt (slow but free).
    A random 64-char string without t1 = online key = no decryption yet.
  • No brute-force, ShadowExplorer, or “.eemv repair” utilities work—the malware deletes VSC, wipes free-space, and rewrites large portions of files with random bytes before encryption.
  • Option for online-key victims: save a pair of an original (pre-attack backup) + encrypted copy + personal ID; if researchers ever obtain the seized key-set you will be able to unlock.
  • Recovery without decryption: restore from immutable/cloud backups (Wasabi, Azure Blob with versioning, Veeam hardened repo), or rebuild from M365/OneDrive “Files Restore” (check time-stamp prior to the *.eemv date).

4. Other critical information

  • Ransom note demands: $999 → lowered to $499 if contact occurs within 72 h; e-mails in _readme.txt are usually [email protected] & [email protected].
  • Data-leak site: DJVU family is “no leak”; they do not exfiltrate—only encryption—so breach-disclosure laws usually not triggered (verify no RedLine stealer pre-activity).
  • Differentiator:
    – Drops updatewin.exe that installs a second-stage loader (PCASTLE) which pushes Proxy Trojan and有时是STOP-Djvu更新器 itself—double-check for backdoors even after decrypting.
    – Installs a root certificate fake2CA.crt → be sure to reset browser cert-store and review proxy settings.
  • Wider impact: DJVU remains #1 consumer ransomware by volume (≈60 % of consumer submissions in 2024 Q1). Corporate networks are rarely disrupted en-masse—but single-user devices get hit, then harvested credentials are sold; expect follow-up phishing or Business-Email-Compromise cases weeks later.

Stay safe—patch early, back-up often, and never download “cracked” software.