djvus

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .djvus
    Files encrypted by this variant are consistently appended with “.djvus” (lowercase) after the original extension, e.g.,
    report2024.xlsx → report2024.xlsx.djvus

  • Renaming Convention:
    The malware does not alter the base filename or original extension; it simply adds the new “.djvus” suffix.
    In some cases an additional ID string (alphanumeric 40–64 chars) is placed between the original name and the new suffix:
    photo.jpg.[7F3E9D2E].[djvus].

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    First publicly confirmed samples were uploaded to early February 2019 (shortly after DJVU/STOP v050 was released). Wave 2 and automation toolchains expanded in March–April 2019. Large-scale outbreaks in South-East Asia, South America, and Eastern Europe occurred through mid-2019, then sporadic clusters ever since.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Malvertising & Cracked Software Bundles (fake keygens/cracks, WinRAR, Photoshop, Fortnite cheats).
  2. Spam/Phishing Emails – zipped attachments posing as invoices, court notices, or DHL tracking PDFs hosting a small downloader.
  3. EternalBlue (MS17-010 disabled by default since 2019) used only by earlier samples; SMBv1 exploitation is now rare.
  4. RDP brute-force & exposed RDP (port 3389) when dropped by secondary bots (e.g., Phorpiex).
  5. UAC-bypass + PowerShell scripts autoload the final payload via scheduled task.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    • Patching: Windows Update > KB4474419 / KB4490628 and MS17-010 (for full kill-chain coverage).
    • Disable PSExec/WMI, limit privileged RDP, enforce MFA for remote logon.
    • Application whitelisting (AppLocker, WDAC).
    • Disable SMBv1 (Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol).
    • Block common dropper extensions (.exe, .com, .scr, .pif in mail gateways).
    • Email containment (sandboxing attachments, DMARC, SPF, DKIM).

2. Removal

  • Step-by-Step Infection Cleanup:
  1. Isolate machine (pull network cable / disable Wi-Fi).
  2. Identify & kill malicious services:
    • taskkill /f /im helper.exe,
    • taskkill /f /im build.exe,
    • any unfamiliar %LocalAppData%\[rstrandomname]\updatewin*.exe.
  3. Delete persistence:
    • schtasks /delete /tn "Time Trigger Task"
    • Registry keys: HKCU\Software\Microsoft\Windows\CurrentVersion\Run → “SysHelper”.
  4. Run Windows Defender Offline scan.
  5. Backup encrypted “*.djvus” files before deletion.
  6. Import backup or image: re-image/reinstall if backup unavailable.

3. File Decryption & Recovery

  • Recovery Feasibility:
    “.djvus corresponds to STOP/DJVU **old_offline key generation (v050 / 2019) and therefore ONLINE keys ≥ v170+ (2020→now).”
    • *If infection occurs offline* (the malware could not call its server), an offline key is used → public release decryptor available.
    • If online key → impossible to decrypt without the private server key at this time.

  • Decryption Tools:

  • Emsisoft STOP/DJVU decryptor (v1.0.0.22+ supports djvus offline key set). Feature “[Key Existing.Database]?” will indicate whether a match exists.

  • Shadow Explorer / Previous Versions for unencrypted copies.

  • Recuva, PhotoRec, R-Studio for “clean” sectors if “_o” / “.bak” versions remain.

  • Essential Patches/Updates
    • OS: 2023-05 cumulative (latest)
    • AV engine signatures: Microsoft Defender client & cloud “Ransom:Win32/StopCrypt”.
    • Browser: Chrome ≥ 114, Firefox ≥ 113 (sandbox exploit mitigations).
    • .NET 3.5 / .NET 4.8 January 2023 patch (prevents reflective POCs).

4. Other Critical Information

  • Behavior Highlights / Distinguishing Traits

  • DJVU variants drop info.txt + _openme.txt ransom notes in every folder, containing the static Tor payment portal (ig6o6menshvvqmbk.onion).

  • Additional surveillance/backdoor: installs Amadey loader, Azorult stealer, and Vidar in 90 % of 2022–23 builds.

  • CPU-cycle-light (no file-shredding, no MFT wiping) to stay below AV heuristics.

  • Checks system locale/language; skips infection in CIS countries (Russia, Belarus, Kazakhstan etc.).

  • Broader Impact

  • >310,000 reported infections worldwide (BleepingComputer datasets).

  • SME / SMB hit hardest: fake K-Meta ransomware removal tools, fake Windows 11 activators have seeded second-wave outbreaks when users tried to undo the encryption.

  • Law-enforcement takedown of the MegaCortex backbone in 2021 did not interrupt STOP/DJVU (separate infrastructure).

Final Advice: Treat .djvus as a dual-parasite (malware loader + ransomware). Even if decryption succeeds incidentally, presumed attackers may still hold credentials via Azorult. Full credential audit and enterprise-scale password reset is mandatory.

(Information last updated: July 2024)