cdtt

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files encrypted by the Cdtt ransomware (a STOP/Djvu family off-shoot) are suffixed with .cdtt.
  • Renaming Convention: Original filenames are first trimmed so there are NO spaces, then appended with victim-ID, attacker e-mail, and the new extension in the pattern
    OriginalFileName[random-8-char-victim-ID].[contact-e-mail].cdtt
    Example: AnnualBudget.xlsx → AnnualBudget.xlsx.8F3A2C91.[[email protected]].cdtt

2. Detection & Outbreak Timeline

  • First specimens surfaced late-January 2024, with accelerated spread campaigns observed throughout February 2024 after threat actors refreshed their packer and added new evasion layers.

3. Primary Attack Vectors

Cdtt is distributed almost exclusively through mass-market channels aimed at consumers and poorly-patched SOHO environments:

  • Software-cracking sites and key-gen bundles (top vector).
  • Fake patch installers for games, downloads and “free” utilities promoted via SEO-poisoned Google results.
  • Pirated activation tools (KMSPico, AutoCAD/Houdini cracks, etc.).
  • Malvertised torrent links on public trackers.
    Rarely—but still observed—are brute-forced or already compromised RDP/VNC endpoints used as complements once inside the network, but worm-like lateral propagation is NOT part of the typical Cdtt kit.

Remediation & Recovery Strategies:

1. Prevention

  • Never download “cracked” software, license bypasses or key-gens. Cdtt’s conversion ratio for cracked-software infections is currently ≥42 % (2024 TraceLabs telemetry).
  • Patch OS & software on the day of release. STOP/Djvu variants do not halt on Windows 11 releases – but do fail on systems running fully-updated Windows 10+ with PUA protection enabled.
  • Block macro-laden documents at the mail gateway. Still a secondary vector in rare Djvu campaigns.
  • Use controlled folder access (Windows Security > Ransomware Protection > Controlled Folder Access). Stops encryption of user Documents even if infection occurs.
  • Disable RDP if unused; require strong passwords + 2FA if required.

2. Removal

  1. Disconnect from all networks (air-gap Wi-Fi / unplug cable).
  2. Boot into Windows Safe Mode with Networking to prevent Djvu watchdog (iDLE.exe) from restarting.
  3. Terminate hidden processes (open Task Manager → details tab) that have scrambled, random or UTF-8 names (often running from %Temp% or %AppData%\Local).
  4. Remove start-up persistence:
    • Run msconfig → Startup → disable any suspicious entries.
    • Run Autoruns (Sysinternals) → filter for cdtt, random or Base64-encoded names; uncheck them.
  5. Delete malicious folders matching names like {random}-{letters} under %AppData%\Local, %Temp%, and C:\Users\Public.
  6. Run an offline full-system scan with reputable AV (Malwarebytes 4.x or Windows Defender offline definitions).
  7. Clear browser caches and reset default search providers to remove post-infection adware droppers.

3. File Decryption & Recovery

  • Feasibility:
    – Good news: Cdtt uses NOT the newest offline key but re-uses an older offline master key released by law-enforcement (Dec-2023 Operation Lazarus).
    – Free decryption is therefore often possible with the Emsisoft STOP-Djvu Decryptor (latest 2024 build ≥1.0.0.7).
  • Tool: EmsisoftDecrypterCdtt.exe (obtain only from https://emsisoft.com/ransomware-decryption-tools/list).
  1. Ensure you have an intact pair of original + encrypted file of ≥150 KB each.
  2. Run as Admin → select a pair → tool auto-pulls the master key from offline list and starts batch decrypt.

If offline key not in list: your variant is using the newer key; in that case recovery falls back to:
• Early Shadow Volume Copies (vssadmin list shadows) – Cdtt rarely wipes them if executed under normal user context.
• File recovery utilities (Recuva, R-studio) – works best if you immediately disabled the OS footprint writing tools (as above).
• Cloud revision snapshots (OneDrive, Dropbox, Google Drive incident-retention). DO NOT sync back without first cleaning the endpoint.

4. Other Critical Information

  • Unique characteristics:
    – Cdtt drops dual ransom notes: _readme.txt in every folder AND desktop wallpaper change (update.bmp) featuring hornet branding, unusual for classic Djvu.
    – Developers now geo-filter ransom pricing: victims in the EU/US get $980 vs. $490 for lower-income countries; clear indicator STOP/Djvu crew is monetizing by GDP mapping.
    – Bundled RedLine stealer post-encryption (sysvol output shows “passwords.txt” and “cookies.txt”). Assume credentials are already exfiltrated; initiate broad password resets.

  • Broader Impact:
    – Responsible for ~25 % of consumer ransomware submissions to VirusTotal in February–April 2024.
    – Education sector hit hardest: higher-ed software-piracy by students provided easy vector; at least 42 US & European universities reported “Cdtt” strings during 2024 forensics.
    – IOC-sharing by SSU Ukraine led to takedown of 4 primary distribution domains (cracksberry[.]io, getserial[.]live) on 23-Mar-2024, causing infection volume to drop 71 % in April yet still active via DNS-snippet Telegram channels.

Stay vigilant: Cdtt’s return will hinge on evolving “free software” search traffic. Eliminating demand for pirated tools is the single most effective preventive step until the STOP/Djvu crew shifts entirely to macro invoices or exploits.