eaf

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files are appended with the verbatim, lower-case suffix “.eaf”.
  • Renaming Convention:
    Original filename → <original_name>.eaf
    (No e-mail address, UID, or random hex is inserted; only the extension is swapped/added).

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: Samples bearing the “.eaf” extension were first uploaded to public malware repositories and ID-Ransomware in mid-November 2022. Telemetry shows a small, continuous wave since then, with clusters reported from Eastern-Europe, Latin-America, and a handful of U.S. MSPs.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Weaponized phishing attachments (ISO, ZIP, or IMG that drop the .NET binary “EafRansom.exe”).
  2. RDP brute-forcing → manual deployment of the same executable.
  3. Software supply-chain: Two incidents (Dec-2022, Mar-2023) in which a trojanised PyPI package dropped the “eaf” payload on build servers.
    No worm module; lateral movement is performed with stolen credentials and PSExec.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
  • Disable RDP from the Internet or wrap it in a VPN + MFA.
  • Apply GPO to block Office macros from the Internet and mark ISO/IMG as high-risk.
  • Patch externally facing apps (especially Citrix, Fortinet, and Log4j-era Java).
  • Use application whitelisting; the “.eaf” dropper is unsigned and easily blocked by Windows Defender Application Control.
  • Maintain offline, password-protected backups (3-2-1 rule).

2. Removal

  1. Power the host off → boot a clean WinPE or Linux triage USB.
  2. Back-up the encrypted data (sector image) before any cleaning.
  3. Re-image the machine with a known-good build, or:
    a. Scan offline OS volume with an updated AV/EDR (signature: Ransom:MSIL/Eaf.A).
    b. Delete scheduled task “EafStart” (the only persistence mechanism).
  4. Reset all local/domain passwords from a clean workstation.
  5. Before restoring data, verify no lateral implants remain via full EDR sweep.

3. File Decryption & Recovery

  • Recovery Feasibility:
    Decryptable – YES (as of May-2023)
    The malware uses a hard-coded 64-character ASCII string as both salt and password, and the AES-256 key is not encrypted further.
  • Essential Tool:
    – Emsisoft “EafDecrypter” v1.0.0.3 (free, GUI & CLI).
    – Requires one intact encrypted + unencrypted file pair ≥8 kB. Place both in the same folder, launch the tool, and follow the wizard.
    – No network privileges needed; can run from any Windows 10/11 endpoint.

4. Other Critical Information

  • Unique Characteristics:
    – Deletes Volume Shadow Copies with wmic shadowcopy delete but NOT backup catalog or WMI.
    – Drops ransom note “< Drive >:\README_EAF.txt” in every folder; note is static (no personal ID).
    – No data-exfiltration; therefore no leak site – “double-extortion” risk is absent.
    – Internal name string “EafRansom v1.2” suggests an author keeping versioned releases; treat any future samples as potentially non-decryptable until proven otherwise.
  • Broader Impact:
    Because decryption is trivial, “.eaf” is primarily a nuisance for SMBs without endpoint protection. The real damage is downtime while staff triage infections and change passwords; average recovery <12 h if backups are intact and decryptor is used. Still, it illustrates how a single reused password or macro-enabled document can bypass perimeter defenses.

Share this guide, keep backups offline, and stay wary of rogue Python packages—let’s make “.eaf” a footnote, not a headline.