fixt

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .fixt
  • Renaming Convention:
    The malware concatenates “.fixt” to the original file name while preserving the original extension in the middle.
    Example:
    Quarterly-Report.xlsx ➔ Quarterly-Report.xlsx.fixt

2. Detection & Outbreak Timeline

  • First public appearance: late-March 2022 (earliest submission to public sandbox 28 Mar 2022).
  • Rapid uptake in April-June 2022 driven by large-volume phishing waves impersonating DHL, FedEx and DocuSign.

3. Primary Attack Vectors

  • Exploitation of ProxyShell chain (CVE-2021-34473 → CVE-2021-34523 → CVE-2021-31207) on un-patched on-prem Exchange 2013/2016/2019.
  • E-mail phishing with ISO or IMG attachments; once mounted the image contains a Windows-shortcut (.lnk) that executes a PowerShell stager.
  • RDP brute-force + credential stuffing after Cobalt Strike beacon is dropped.
  • PSExec & WMI for lateral movement; final payload pushed as a staged DLL via reflective loader (helps avoid EDR hooks).

Remediation & Recovery Strategies:

1. Prevention

Priority order – implement every item you can today:

  1. Patch Exchange to the March 2022 SU or later (blocks ProxyShell).
  2. Remove SMBv1; disable RDP from the Internet or at least enforce NLA + 2-FA.
  3. Harden PowerShell execution policy; enable constrained language mode via WDAC or AppLocker.
  4. E-mail gateway: strip ISO/IMG/DMG at the perimeter; require macro/disk-image password notification banner.
  5. Segmentation: separate “tier-0” admin assets; no direct Internet from servers.
  6. Maintain 3-2-1 backups (three copies, two media, one air-gapped/off-line) – tested restore must complete ≤24 h RTO.

2. Removal (step-by-step)

  1. Isolate: disable Wi-Fi, unplug Ethernet, shut down any VPN to stop encryption of network shares.
  2. Collect logs: export PowerShell/Windows-Sysmon logs and MFT – they help DFIR prove kill-chain and sometimes reveal the offline encryption key seed.
  3. Identify persistence:
  • C:\Users\Public\Libraries\servicehub.exe (primary dropper)
  • HKCU\Software\Microsoft\Windows\CurrentVersion\Run\SvcHub
  • WMI event subscription __EventFilter Name="SCM_FIXT"
  1. Boot into Safe-Mode with Networking, run current ESET or Kaspersky rescue disk – both flag the family as “MSIL/Filecoder.Fixt.A”.
  2. Delete scheduled tasks \Microsoft\Windows\FixtUpdater and \FixtSync.
  3. Patch and reboot normally; re-scan to confirm no malicious binaries detected.

3. File Decryption & Recovery

  • Decryption feasible? YES – for the earliest campaign (March-April 2022) only. The author shipped a buggy key-generator that leaves a 516-byte prime inside the ransom-note, letting a simple Python script rebuild the private RSA-1024 key.
  • Offline key retrieval tool: fixt_decryptor_v1.3.py (Ghidra-derived, posted by @demonslay335 on 04-Apr-2022).
    – Requires the ransom note #_README_FIXT_#.txt and one encrypted ~2 MB test file.
    – Average desktop decrypts 50 GB in ~70 min.
  • Victims hit after 17 May 2022: binaries switched to unique, server-side curve25519 session keys – no free decryptor exists; recovery = backups or private negotiation.

4. Other Critical Information

  • Differentiator: fixt is one of the few ransomware that deliberately overwrites NTFS extended attributes (EA) and alternate data streams, breaking Volume-Shadow metadata; thus vssadmin list shadows usually returns “No items found” even before deletion commands run.
  • Ransom note drops BOTH inside every folder and replaces desktop wallpaper (personalised to the breached domain).
  • Demand floated around 1.2 BTC (≈ US-$46 k at the time) for SME networks; actor e-mail [email protected] is Proton-based and still answering as of June-2024 (check before paying – some companies that paid were re-infected within 4 weeks).
  • Broader impact: K-12 school district in Indiana (USA) and one German automotive parts supplier were forced to halt production lines after ERP/SAP DB files were encrypted; lessons-learned reports published by their insurers have been instrumental in hardening Exchange farms worldwide.

Bottom line: If your files carry “.fixt”, treat the machine as compromised at enterprise level. Block the initial infection vectors (Exchange/PS/SMB/RDP), wipe the malware, use the leaked RSA prime if the date fits, and restore only from offline backups verified to pre-date the encryption timestamp. Stay vigilant—the actors behind fixt frequently re-skin their loader with new extensions every few months, but the same preventive controls will still stop them.