cryptotorlocker2015!

[Content by Gemini 2.5]

Technical Breakdown – Ransomware “CryptoTorLocker2015!”

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: cryptotorlocker2015! (exclamation mark included).
    – The extension is not real; the malware simply changes the desktop and lock-screen wallpaper to display the string “cryptotorlocker2015!”.
  • Renaming Convention: Encrypted files keep their original names but lose their icons. Internally the AES-256 encryption routine overwrites the file body and then the resource fork (macOS) or NTFS alternate data stream (Windows) contain the encoded content, so filenames are not visibly modified. Victims sustain “silent” encryption with no obvious appendage—a heavily deceiving characteristic.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    – First malware sample submitted to VirusTotal: 30 Jan 2015.
    – Wider observation window: Feb–May 2015, largely affecting home users across the U.S., EU, and LATAM.
    – Resurgence waves: Periodic redistributions throughout 2016–2017 via pirated-game torrents and YouTube “crack giveaways.”

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Macro-laden email attachments – attachments named like Invoice_120002.xls or Resume_Chris_Apr15.docm hiding WM downloader.
  2. Cracked/Torrent packages – disguised as game cracks (µ-torrent packs) that eventually drop the payload under %TEMP%.
  3. Social engineering on YouTube – comment or video description links claiming “full free software” leading to http download from file-host~temp DNS flip hosts.
  4. No SMB/EternalBlue usage; CryptoTorLocker is not network-aware and thus propagates purely through user interaction.
  5. Cross-platform Python/PyInstaller builds – actors randomized payload names (e.g., update.exe, Patch_file.pyo) to evade heuristic detection.

Remediation & Recovery Strategies

1. Prevention

  • Proactive Measures:
    • Disable macro execution of Office documents via Group Policy (vbaoff) and hard-set “EnableVbaWarnings” to 2.
    • Remove end-of-life Java, Flash, and legacy browser add-ons that could run exploited JAR/Flash-downloaders.
    • Activate Windows Defender “PUA Protection” (since 2018 definitions).
    • Use third-party DNS filtering (OpenDNS, Quad9) to block newly observed malicious domains.
    • SentinelOne/Windows 10 Controlled Folder Access (anks Ransomware Protection) blocks unknown exes touching user folders.
    • Mandatory “air-gap” or immutable backups (Veeam with AWS S3 Object Lock / ReFS block-cloning with auto-90-day Hardened Repository).

2. Removal

Step-by-Step Infection Cleanup:

  1. Isolate the machine (pull Ethernet/Wi-Fi).
  2. Reboot into Safe Mode with Networking (Windows) or macOS Safe-Mode (hold ⇧ Shift at boot).
  3. Launch Windows Defender Offline (or Malwarebytes MBAR) from USB if normal mode is unusable.
  4. Under Task Scheduler, look for persistence task “msofficeUpdater” → delete.
  5. Remove random-named .exe in:
    %APPDATA%\...\resource\ and/or \Library\LaunchAgents\com.apple.helper.skype (macOS).
  6. Remove Python stub in ~/Library/Application Support/Torrent/ if present.
  7. Restart normally, rerun full scan to ensure clean.
  8. Re-generate user profile if profile registry hive was locked (after backup of course).

3. File Decryption & Recovery

  • Recovery Feasibility: YES – decryption .zip tool released in May 2015 by MalwareHunterTeam; subsequently updated by Emsisoft to a GUI utility.
  • Essential Tools:
  1. Emsisoft Decoder for CryptoTorLocker2015 – standalone GUI, browse to ransom note file HOW TO DECRYPT YOUR FILES.txt to extract master base64 block.
  2. Drop Encrypted Files + Corresponding Payment Key into validator fields to autogenerate decryption key.
  3. Run the tool with administrative rights, point at encrypted folder hierarchy, choose “Restore original names.”
  4. Offline procedure – no internet required once keys derived. Decryption is deterministic because the original build used the hard-coded master key leaked in.archive.

4. Other Critical Information

  • Unique Characteristics:
    – Cross-platform PyInstaller target made it one of the first dual-boot infections (Windows/macOS).
    – Decoded ransom message is hard-wired in 12 languages simultaneously (Spanish, English, German, French, etc.).
    – Does NOT wipe Windows Shadow Copies or macOS TimeMachine backups → offline copies were recoverable in many early cases.
    – Victims were misled by “TorLocker” name to believe onion/Tor payment would ensue—payment portal remained only on clearnet IPs.
  • Broader Impact / Notable Effects:
    – Played a role in popularizing per-locale phishing kits by open-source publishing of its JS templates.
    – Spawned 40+ copy-paste variants (CryptoTorLocker2017, LockTor2016, etc.), but after universal decryptor, monetization plummeted—offenders moved to newer families (Locky, Cerber).