djvuq

[Content by Gemini 2.5]

Title: “.djvuq” Ransomware – Technical Dissection and Response Playbook
Variant: DJVU/STOP family, off-shoot #239 (extension “.djvuq”)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    Files are appended “.djvuq” as a SECONDARY extension to the original.
    Example: Quarterly_Report.xlsx → Quarterly_Report.xlsx.djvuq
  • Renaming Convention:
    Original filename is kept in the first portion; nothing is prepended, no email addresses or victim IDs appear in the file name itself (the victim-ID/hash is stored inside the malware’s encrypted key-data file).

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    First sightings late-October 2023; rapid acceleration in phishing-driven campaigns through December 2023. Still circulating via malvertising and cracked-software installers (Jan-Apr 2024).

3. Primary Attack Vectors

| Attack Vector | Details & Typical Use by .djvuq |
| — | — |
| Cracked-software or key-gen downloaders | Bundled in “free” Adobe/AutoCAD/{game} activators hosted on Discord, GitHub-look-alikes, Lokibot DLL side-load. |
| Malicious ads (maldvert) | Fake Firefox/Edge updates leading to rogue update.exe → .NET loader → djvuq core. |
| Pirated e-book & media torrents | Common vector – it drops via PowerShell scheduled-task persistence. (NOT via EternalBlue or SMB exploit; affects only user space.) |
| Email phishing | Lower share; uses IRS/Amazon refunds lures with ISO lnk file, launches wscript→dllhost chain. |

Remediation & Recovery Strategies

1. Prevention – “First 5” Must-Haves

  1. Kill cracked-software/sys-keygen sources – block torrent/Tor-Mirror categories at web-proxy.
  2. Disable or severely restrict Windows Script Host – enforce Applocker/WDAC rule: powershell.exe -ExecutionPolicy Restricted.
  3. Patch browsers & .NET runtimes – djvuq exploits MSI install chain via CVE-2023-36884.
  4. Deploy endpoint agent with Script-Level & Exploit-Rule coverage (Microsoft Defender for Endpoint, SentinelOne, CrowdStrike-Script Control).
  5. Enforce least-privilege + Software Restriction Policies – deny C:\Users\*\Downloads\*.exe execution.

2. Removal – Step-by-Step

  • Phase 0 – Contain: Disconnect host from network (air-gap physical or VLAN).
  • Phase 1 – Identify loader:
    a) Launch Process Explorer or Autoruns64.exe → look for suspicious ‘rundll32.exe’ under %userprofile%\AppData\LocalLow\*.tmp or folder path with high-entropy alphanumeric string (e.g., C:\Users\xyz\AppData\LocalLow\7e3a28f0\tmp123.tmp.dll).
    b) Collect the _id.djvuq file (metadata) for later analysis at VirusTotal.
  • Phase 2 – Kill the process:
    taskkill /f /im <randomname>.tmp or if locked, boot to WinRE → offline removal.
  • Phase 3 – Scheduler & Registry cleanup:
    a) Delete registry entry at HKCU\Software\Microsoft\Windows\CurrentVersion\Run → value “SysHelper” or “winlogin” pointing to the above dll.
    b) Remove scheduled task(s) named “ServiceProcess”, “Driver Updates” by running (elevated):
    schtasks /delete /tn "*updates*" /f.
  • Phase 4 – Forensic isolation:
    Save memory dump and disk-image of the user portion before rebuilding.
  • Phase 5 – Fresh OS or Roll-back:
    Re-image the workstation from known-good offline backup; scan all user-writable shares to ensure propagating MSPack/ .xz archives are gone.

3. File Decryption & Recovery

  • Recovery Feasibility:
    • Partially Possible – STOP/DJVU encrypts with offline key when C2 fails; if your _id.djvuq file matches an “offline” ID ending in t1 (look for the string t1 at offset 0x03E328), use Emsisoft STOPDecrypter.
    • Not feasible – C2 returned a fresh online key? A true brute-force is cryptographic non-viable. Check the Emsisoft tool’s nightly database for a published key.
  • Official Decryptor Links:
  1. Emsisoft STOPDecrypter (actively updated): https://emsisoft.com/ransomware-decryption-tools/stop-djvu
  2. JDSecurity decrypt_STOPDjvu.exe – experimental parser for R# algorithms but often slower than Emsisoft.
  • Offline-ID test: PowerShell snippet to extract: 
$bytes = [IO.File]::ReadAllBytes("$Env:USERPROFILE\_id.djvuq");  
$idHex = [System.BitConverter]::ToString($bytes[250..260]) -replace "-",""  
if ($idHex.ToLower().EndsWith("7431")) {Write-Host "Offline key detected - decryption possible"} else {Write-Host "Online key - await disclosure or restore backups"}

4. Other Critical Information

  • Differentiators:

  • .djvuq updated the packing algorithm to use ChaCha20-SIV instead of Salsa20 (Speed-up aimed at legacy HW).

  • Drops two separate binaries: Windows variant + an obfuscated macOS .bundle for BigSur+ suggesting tentative Apple-port testing; however has not yet seen live macOS campaigns.

  • Writes a secondary ransom note info.hta AND ReadMe!.txt in every folder – watch for @firemail(.)cc contact.

  • Broader Impact / Notable TTR (Time-to-Ransom):

  • Average TTR from infection notice to finished encryption across observed campaigns: 3 min 28 s on 12 TB file shares.

  • Heavily seeded in Eastern-Europe, MENA & SEA regions using geo-distributed Git-LFS URLs (abusing open-source mirrors).

TL;DR Action Card (print & pin on SOC desk)

  1. Quickly isolate → confirm .djvuq files & _id.djvuq metadata.
  2. If offline-ID → run Emsisoft decryptor immediately. Otherwise initiate recovery via backups/clean images.
  3. Permanently block user-executable downloads and cracked-ware sites.
  4. Push PowerShell hardened execution policy via GPO.
  5. Red-team run phishing + fake-cracked installer simulation quarterly.

Stay vigilant – the STOP/DJVU actors rebuild a new extension every ~10 days; monitor for *.djvuq, *.tro, *.mmvb, …