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RANSOMWARE SPOTLIGHT – DJVUR (a.k.a. STOP / Djvu family)

TECHNICAL BREAKDOWN

1. File Extension & Renaming Patterns
   • Confirmation: .djvur (all lower-case)
   • Renaming Convention:
   ORIGINAL_NAME.ext → ORIGINAL_NAME.ext.djvur
   – no prefix, no UUID, nothing else is touched; the only visible change is the double extension.

2. Detection & Outbreak Timeline
   • First orphaned sample submitted to ID-Ransomware: mid-March 2021 (clustered variants then cascaded through April).
   • Usage spiked again in 2022–2023 waves tied to adware bundles pushing cracked software (OBS Studio “crack”, Adobe Illustrator “patches”, KMS activators).
   • Continues as the most common STOP vector globally; new flavours (`.aa, .bbw, .qlln, etc.) are re-brands rather than rewrites, so .djvur advisories stay valid for the entire STOP/Djvu family.

3. Primary Attack Vectors
   • Pirated or cracked software (most frequent).
   – Fake keygen/activators (KMS Auto, AutoCAD).
   – “Optimized” game installers (GTAV, Photoshop, film torrent bundles).
   • Benign-looking ZIP attachments in e-mails—often posing as invoices in DHL/UPS lure campaigns.
   • Exploit kits occasionally tie in EternalBlue wrappers or RDP bruteforce → manual drop via Mimikatz for enterprise hit-and-run events, but 80 % of all cases remain consumer endpoints obtained via crack downloads.
   • Secondary loader chain: Amadey bot/Azorult stealer → STOP payload for data theft + encryption in one hit.

REMEDIATION & RECOVERY STRATEGIES

1. PREVENTION
   • Block execution from %AppData%\Local\Temp\ and %ProgramData%\ via Windows Defender ASR rules.
   • Force execution-policy “Restricted” for PowerShell; block .ps1 e-mail attachments.
   • Patch the underlying CVE that some bundles still probe:
   – CVE-2017-0144 (EternalBlue) – March 2017 MS17-010.
   – Discontinue SMBv1.
   • Disable RDP or require NLA, strong passwords + MFA.
   • Application whitelisting (WDAC / AppLocker) to stop the “random-name.exe” signed with fake/signed stolen certs.
   • Offline backups on rotating media with versioning (Veeam, Macrium Reflect, Tandberg RDx).

2. REMOVAL IN DETAIL
   • Disconnect from all networks (ethernet + Wi-Fi).
   • Boot into Safe Mode + Networking.
   • Run Malwarebytes 4.x or ESET Online Scanner – both detect DJVUR variants as Ransom.Win32.STOP.gen with >99 % TP.
   – Delete scheduled task called “Time Trigger Task” (GUID name) in Tasks\Microsoft\Windows.
   – Kill the helper service “updatewin.exe” (signed: SATURN LLC).
   • Use AdwCleaner to remove bundled adware responsible for re-infection.
   • Clear every “_readme.txt” dropper.
   • Post-cleanup: run sfc /scannow or “DISM /Online /Cleanup-Image /RestoreHealth” if system files damaged.

3. FILE DECRYPTION & RECOVERY
   • No universal decryptor exists for .djvur with online keys.
   – DJVUR forks into offline (fixed key) vs. online (per-victim RSA-1024) mode.
   • Check immediately with the Emsisoft STOPDecrypter (current 1.2.0.0):
   – Drop one encoded file + ransom note into the tool → it tells you which mode.
   – If OFFLINE: tool will automatically decrypt.
   – ONLINE: the tool saves the encrypted variant + your “.KEY” file; submit to Emsisoft via forum ticket – occasionally they collect leaker keys (2022 leak yielded ~230 keys).
   • Shadow Copies: STOP deletes VSS storage via vssadmin delete shadows /all, but Reboot into WinRE → shadow-copy dismount & scan occasionally finds older snapshots.
   • Volume-cavity carving (Photorec, GetDataBack) can scrape partial files with fragments of prior versions.
   • If no backups & offline key not released: the victim community consistently discourages paying – key turnaround average 48 h, still 60 % chance corrupted.

4. OTHER CRITICAL INFORMATION
   • Unique Trait: Every STOP build schedules the exact same task (“Time Trigger Task”) which re-launches a copy under %localappdata% > sub-folder like iqec371t, rbd638.cfg, etc. Knowing the static name brings immediate IOC edges.
   • Tightly bundled adware behaviour: sample “djvur-earl.exe” drops BrowseFox, Segurazo, TaskbarSystem, cluttering endpoints for mass spyware exfil even after decryption.
   • Broader Impact: DJVUR is currently the most logged strain on ID-Ransomware (>38 % of 2023 submissions). It’s primarily consumer, but SMBs with BYOD culture are seeing 2–6 % of endpoints per incident. Successful decryption + nulled reinfection risk lowers average downtime from 7 days to 10 h if offline-key remediation possible.

Strike back: Patch the path you use before launching cracked software; if you must run untrusted EXEs, do so in an isolated Hyper-V sandbox and always keep an immutable backup.