djvut

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The Djvu ransomware family appends the exact extension “.djvu” (or one of its look-alikes such as “.djvut”, “.rejg”, “.mpal”, “.lalo”, etc.) to every encrypted file.
  • Renaming Convention: {originalFileName}.{originalExtension}.djvut – for example Budget-2024.xlsx becomes Budget-2024.xlsx.djvut.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: Djvu variants (including .djvut branches) began being actively distributed late-2018 as part of the larger STOP/Djvu campaign. Peak activity waves occurred Q3-Q4 2019, 2020, and 2021, and new offshoots (including .djvut) still emerge monthly via cracked‐software forums and spam campaigns.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Malicious installers masquerading as pirated/cracked software (compilers, keygens, game mods, Adobe cracks, Windows activators) – distributed via torrents, shady download portals, YouTube links, Discord “free software” channels.
  2. Email & messaging spam with password-protected ZIP attachments or embedded Google-Drive/OneDrive links.
  3. Exploit kits (RIG, Fallout) when users land on compromised websites loaded through malvertising.
  4. Poorly secured Remote Desktop Services brute-forced or credential–stuffed; once in, the attacker manually drops the Djvu loader.
  5. Drive-by downloads via fake codec/update pop-ups.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
  • Block cracked software: Use application-control/endpoint defense that prohibits running unsigned executables in %TEMP%, %userprofile%\Downloads, Desktop, etc.
  • CVE-2017-0144 (EternalBlue) & SMBv1: Disable SMBv1 via GPO, apply MS17-010/TurnOffSMB1 PowerShell directive.
  • Email hygiene: Strip executable content in ZIPs, enable SPF/DKIM/DMARC, sandbox attachments.
  • Least privilege & MFA: Restrict local admin rights; enforce MFA on RDP and VPN accounts.
  • Segment IoT/home devices from high-value hosts; use DNS-layer filtering (Quad9, Umbrella) to block known C2 domains.
  • Offline, immutable backups with 3-2-1 rule: 3 copies, 2 media types, 1 offline/off-site.

2. Removal

  • Step-by-step Cleanup:
  1. Isolate the infected machine(s): unplug network/Ethernet, disable Wi-Fi.
  2. Boot into Safe Mode with Networking or use MS Defender “Windows Defender Offline”.
  3. Manual & tool inspection:
    • Run ESET Online Scanner, Malwarebytes 4.x, Kaspersky Virus Removal Tool – they target the updatewin.exe / _readme.exe (Djvu installer) and its scheduled tasks under C:\ProgramData\Microsoft\Windows\SystemData or %APPDATA%\{random-name} folders.
  4. Delete malicious services and scheduled tasks (schtasks /query /fo TABLE > verify and delete).
  5. Patch or remove the entry vector (cracked program, vulnerable RDP, mail-infected attachment).
  6. Reboot into normal mode and run a second scan to confirm cleanup.

3. File Decryption & Recovery

  • Recovery Feasibility:
  • < 50 % chance STOPDecryptor can help: If the malware was configured to use OFFLINE encryption (presence of id-[8-hex-digits].{email@…}.djvut in ransom note) files may be recoverable.
  • Latest variants use ONLINE keys: The attacker-controlled RSA-1024 key makes traditional decryption impossible; only pay-ransom or backups.
  • Essential Tools/Patches:
  • Emsisoft STOP/Djvu Decryptor – most recent version as of 2024-06.
  • Windows Defender updates ending in 1.467.x or newer (adds specific signatures).
  • MS17-010 SMBv1 patch (KB 4012212/4012213/4012598).
  • RDP hardening: KB4499175 (BlueKeep mitigation); enable NLA, restrict port 3389.
  • Credential-dump protection: Enable “RestrictedAdmin” and “Protected Users” GPO to block qusaSR.dll dumped via Mimikatz.

4. Other Critical Information

  • Unique Characteristics:
  • Ransom note: Called _readme.txt (dropped in root and every folder) demanding $980 or $490 in Bitcoin.
  • Network telemetry: Contacts m***w4qvhd.com or n***jteuc.com via HTTP 80/443 (fake Cloudflare payloads).
  • Obfuscation: Uses LOLBins (certutil -urlcache -split -f) to retrieve next-stage payloads under %TEMP%\38defd-123.exe.
  • Persistence tricks: Adds itself to HKCU\Software\Microsoft\Windows\CurrentVersion\RunOnce, copy named updatewin.exe.
  • Broader Impact:
  • Most widely distributed consumer-grade ransomware by early 2020, with >350 sub-extensions spawned.
  • Market effect: Contributed to mainstream adoption of cloud-based immutable backup and zero-trust endpoint products.
  • Psychological toll: Over 75 % of victims still paying because cracked software usage kept their backups non-existent or stale.

Closing Advice: Never rely on decryption keys being released. Replace cracked files with legitimate alternatives, invest in isolated backups, and enable Controlled Folder Access (Windows Defender ASR) to mitigate Djvu’s impact further.