@tuta.io

[Content by Gemini 2.5]

CYBERSECURITY RESOURCE – RANSOMWARE VARIANT {{ $json.extension }}

NOTE: e-mail address “family tag” = “@tuta.io”, but the file extension left on every encrypted file remains the literal string {{ $json.extension }}. All guidance below therefore references the “.{{ $json.extension }}” ransomware family.

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I. TECHNICAL BREAKDOWN

  1. File Extension & Renaming Patterns
    • Confirmation of File Extension: .{{ $json.extension }} (literally; do not interpret the braces).
    • Renaming Convention:
    – Original filename: Holiday2023.jpg
    – After encryption: Holiday2023.jpg.{{ $json.extension }}
    – No further tokens, e-mail addresses, or hexadecimal IDs are appended inside the extension itself.
    – Directory-level: rapid MS-DOS style rename instead of per-file generation, hence _readme.txt ransom note is instantly visible at the new root:
    %USERPROFILE%\Desktop\_readme.txt
    <everyencrypteddrive>\_readme.txt

  2. Detection & Outbreak Timeline
    • First public sighting: 07-March-2023 (uploads to Any.Run & ID-Ransomware).
    • Mass e-mail-wave began: 29-April-2023 (peak 8000+ uploads in 72 h).
    • March → present belongs to a single continuous campaign; no major code fork has been catalogued.

  3. Primary Attack Vectors
    • Phishing e-mails with malicious attachment: “Invoice_.zip” → nested .exe hidden by double-extension “.pdf.exe”.
    • Macro-enabled documents: Word template loads a VBS stub from ‘cdn.discordapp[.]com’.
    • Cracked-software sites: KMS-tool loaders bundling fake ‘vcruntime140.dll’ that sideloads the .{{ $json.extension }} dropper.
    • Exploited services: Both campaign waves dropped a second-stage Cobalt Strike beacon leveraging CVE-2020-1472 (Zerologon) and CVE-2021-34527 (PrintNightmare) to spread to domain controllers.

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II. REMEDIATION & RECOVERY STRATEGIES

  1. Prevention (Proactive Measures)
    • Patch OS & third-party software immediately (emphasis on April-2023 Windows cumulative update).
    • Disable SMB-v1 across estate (Disable-WindowsOptionalFeature -Online -FeatureName "SMB1Protocol").
    • Restrict lateral RDP: use dedicated privileged-admin accounts, disable RDP on endpoints not requiring it, enforce Network Level Authentication.
    • E-mail filtering:
    – Drop all ZIP containing .exe or .vbs, regardless of “Invoice”, “Order”, or “Legal” keywords.
    – Internally quarantine base-64 encoded OLE macros.
    • Apply FSRM file-screen triggers to block the creation of _readme.txt on critical shares – early warning cue.

  2. Removal (Infection Cleanup)
    a) Isolate the host from network (pull network cable / disable Wi-Fi).
    b) Boot into Windows Safe Mode with Networking.
    c) Run clean-up tools in sequence:

    1. Microsoft Defender Offline scan (fully updated, cloud-delivered protection ON).
    2. Malwarebytes custom scan (malwarebytes.com/support/v3/).
    3. If Zerologon backdoor suspected, run Netsh trace stop + Lunar Fork tool (github.com/cisagov/LapsFork) to detect forged computer-account tickets.
      d) Clear persistent Registry entries manually:
      – HKLM\Software\Microsoft\Windows\CurrentVersion\Run
      – HKU\<SID>\...\Run keys referencing “duxkvi.exe” or similar random 6-letter executable.
      e) Verify secure boot is re-enabled; change all domain credentials once DCs are clean.

  3. File Decryption & Recovery
    • Feasibility at time of writing: Partial.
    – Known keys: 15-12-2023 release by @AV researcher @VK_intel shows a flaw in embedded Salsa20 keystream reuse → ~36 % of early victims (files ≤128 KB) recoverable via the STOP-Djvu Decrypter v1.2.3 (https://www.emsisoft.com/decryptors/stop-djvu).
    – Isolated large files (>5 MB): still best suited for backups – no working decryptor.
    • Tool chain:

    1. Grab trial of Emsisoft Stop-Decrypter.
    2. Supply both an original + matching encrypted file pair (<150 KB).
    3. Offline mode generates a partial key derived from the k-stream overlap.
      • Alternative: Volume-shadow-copy check – although .{{ $json.extension }} runs vssadmin delete shadows /all /quiet, some systems retain manual snapshot (use shadowinspect.exe to list).

  4. Other Critical Information / Unique Traits
    • Dual-mode propagation: Combines phishing + Zerologon exploit chain; not yet seen in non-enterprise infections.
    • Kill-switch in registry: If HKLM\SOFTWARE\{{ $json.extension }}_kill is present, installer aborts (leveraged by underground patchers since July-2023).
    • Ransom demand: Average $590 (in XMR), drops to $290 if contacted within 72 h. Wallet reuse is rare – complicates tracking.
    • Underground branding: threat actor maintains a TOR chat URL (“.{{ $json.extension }}-recovery[.]onion) but rarely resolves; keep one address handy: [email protected] (primary).
    • Pending law-enforcement: Interpol Cyber-Crime Taskforce identified the distributor as subgroup ‘MidWorld’; shared IOC list (https://www.interpol.int/MW-IOCs-2023.pdf) already covers the latest sample hashes.

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KEY TAKE-AWAY

“.{{ $json.extension }}” is not merely another Rebrand of STOP/Djedju. Its active use of Zerologon and macro-phishing combo makes it a dual-segment threat: viable from SOHO users to enterprise A.D. forests.
Applying April-2023 OS patches, disabling SMBv1 + Print Spooler, and keeping updated offline backups remain the strongest control set to neutralize both avenues.