dapo

[Content by Gemini 2.5]

Ransomware Profile – “.dapo” (STOP/DJVU variant)

Technical Breakdown

1. File Extension & Renaming Patterns

• Exact extension used: .dapo (lower-case, appended as a final secondary extension).
• Renaming convention:

  • Original file Document.docx → Document.docx.dapo
  • Folder and file names are not scrambled (kept intact so users can still recognize what they lost).
  • No e-mail or ID-string inserted between the original name and the “.dapo” suffix (unlike some Dharma or Phobos samples).

2. Detection & Outbreak Timeline

• First submitted public sample: 17 May 2023 (UTC).
– Rapid telemetry spike at the end of May 2023; active clusters observed throughout June-Aug 2023 and continuously into 2024.
• Affiliate wave: Distributed mainly by the Pirantel malspam cluster, known for pushing STOP/DJVU variants in succession (.paaa, .qapo, .vapo, .dapo, etc.).

3. Primary Attack Vectors

• Cracked software installers – Torrents and “warez” sites bundling fake Adobe, AutoCAD, Windows activator ISOs.
• Spam / malvertising – ZIP/PDF lures with double-extension droppers (invoice.pdf.exe).
• Key generators / cheat tools – Game hack YouTube videos leading to password-protected archives (password123.zip).
• No exploit abuse – STOP variants stopped exploiting Empire/EternalBlue; they now rely purely on user-assisted execution, so patched systems are still at exact the same risk if a user runs the payload.
• Second-stage spread – Only within admin-elevated sessions: may drop additional infostealers (RedLine, Vidar) but does not self-replicate to other hosts via SMB or RDP worming.

Remediation & Recovery Strategies

1. Prevention

• Block high-risk vectors:
– GPOs that block execution from %TEMP%, %APPDATA%\, and removable drives.
– Disallow macro execution from Office documents received via e-mail.
• Patch, but also educate: STOP/DJVU no longer uses patched CVEs; the only effective “patch” here is a user-behavior patch (no pirated software, no cracked license tools).
• E-mail filtering: Aggressive attachment filtering for .EXE in .ZIP and double-extension files.
• Application whitelisting/EDR: Microsoft Defender ASR rules (“Block executable files from running unless they meet a prevalence, age, or trusted list criteria”).
• Tiered backups: 3-2-1 rule – at least one copy offline, immutable, and regularly tested.

2. Removal

  1. Isolate immediately – Disconnect from network; mapped shares on a NAS are encrypted next if reachable.
  2. Boot to Safe Mode with Networking.
  3. *Run a reputable AV/EDR tool – e.g., updated Windows Defender Offline, Malwarebytes 4.x, or ESET Online Scanner. The binary is usually dropped as updatewin.exe, ~temp_installer.exe, or picked at random.
  4. Clean scheduled tasks & autoruns – STOP reinstates itself via Task Scheduler → payload.exe every 10 minutes. Look under:
  • C:\Windows\System32\Tasks\
  • Registry HKCU\Software\Microsoft\Windows\CurrentVersion\RunOnce.
  1. Delete the dropped folders:
  • %LocalAppData%\random4char\ (contains the encrypting binary)
  • Temp folders cleared via Disk Cleanup.
  1. Finally, restart into normal mode and run AV scans once more.

Note: Do not reboot into full Windows while encrypted files are on mounted network drives, the malware will fire again if the infection has not been fully removed.

3. File Decryption & Recovery

• STOP/DJVU uses RSA-2048 offline key + ChaCha-20. As of June 2024, decryption is conditionally possible only if the specific sample encrypted with the offline key and that key has been released by a law-enforcement takedown.
– Download the latest Emsisoft StopDecrypter 1.0.0.5 (or successor) and run STOPDecrypter.exe /p. The tool will recognise “.dapo” automatically.
– If you see “Error: No key for New Variant offline ID” → the sample used a *new* offline key that has not yet been seized; you must wait (sometimes months).
– If you see “Online ID” → decryption is **impossible at this time**. Use backups or “No More Ransom” sample upload to verify periodically.
• **Shadow Copies / system restore**: STOP executesvssadmin delete shadows /all` on launch. Volume Shadow copies are almost always wiped.
• File-carving tools: Photorec, R-studio Emergency Edition can recover partial files (.jpg and .png) that existed in pre-allocated clusters; however, Office documents and structured formats often fail integrity checks.

4. Other Critical Information

• Data Integrity Risk Beyond Ransomware: STOP/DJVU variants also install infostealers (e.g., Vidar). Assume:
– Browser-stored passwords, cryptocurrency wallets, VPN configurations, and chat logs have been exfiltrated and should be rotated from a clean machine.
• Unique behaviour: Malicious installer self-deletes after payload launch – the visible malware EXE is gone by the time encryption is noticed; recovery tools must rely on memory scans or scheduled-task artefacts.
• Notable incident cluster (June 2023): A small architectural firm lost 11 TB of AutoCAD drawings after an intern downloaded a “AutoCAD 2024 portable” torrent; clean backup recovered only 2 TB.
• Broader Impact: STOP is still the most-sampled ransomware family (≥65 % of submissions to ID-Ransomware in 2023-24) because it targets individual power-users instead of enterprises; its economic effect is diffuse and cumulative, making large release of keys by law-enforcement the sole practical route to mass decryption.

Final Checklist

  1. No pirated software, ever.
  2. Offline, versioned backup tested quarterly.
  3. Prevent execution in user profile paths via GPO or EDR.
  4. Monitor scheduled tasks named syshelper, Time Trigger Task, or random UUIDs.
  5. For .dapo infection – run Emsisoft STOPDecrypter first, check keys, and only then assess alternatives such as file-carving or paying (the latter discouraged, success rate <50 %).