fonix

[Content by Gemini 2.5]

Fonix (a.k.a. XINOF, “FonixCrypter”) – Community Response Guide

Last update: 2024-06-01

TECHNICAL BREAKDOWN

1. File Extension & Renaming Patterns

  • Confirmation of file extension:
    .fonix (lower-case, appended to the original name)
  • Renaming convention:
    Original filename → original.name.fonix
    Directory-wide ransom note → Fonix_Data_Recovery.txt (sometimes Help_Data_Recovery.txt)

2. Detection & Outbreak Timeline

  • First public sighting: November 2020 (uploads to ID-Ransomware and MalwareHunterTeam tweet 2020-11-13)
  • Peak activity: Q4-2020 – Q2-2021 (multiple voume-tier Telegram “affiliate” ads, closed Dec-2021 after master-key release)
  • Re-appearance: sparse samples still circulate in 2023/24 via cracked-software bundles, but main botnet is defunct.

3. Primary Attack Vectors

  • Malspam with ISO/ZIP attachments that launch .NET loader (Covenant, BAT > PowerShell).
  • Cracked software/game torrents containing NSIS installer that side-loads Fonix.
  • Exposed RDP (TCP/3389) protected by weak or prior-credential compromise – manual drop of svchost.exe clone.
  • No significant SMB/EternalBlue auto-propagation (unlike WannaCry); Fonix is human-operated post-foothold.

Internals at infection

  • C# binary wrapped with 4-stage PowerShell (living-off-the-land) downloader; payload finally executes with -windowstyle hidden.
  • Kills SQL, Exchange, Oracle, Veeam, backup services; clears VSS with vssadmin delete shadows /all.
  • Uses AES-256-CBC per file (random 32-byte key) → key bundle encrypted by RSA-4096 public key embedded in binary.
  • Deletes itself after encryption but leaves P7tmp.log with enumerated paths (used for affiliate revenue tracking).

REMEDIATION & RECOVERY STRATEGIES

1. Prevention – Top Controls (in order of ROI)

  • Segment & audit RDP: disable if unused, whitelist IPs, enforce 2FA / VPN-first, set “Network Level Authentication”.
  • EDR/NGAV with behaviour rules: block PowerShell spawned by Office/ISO, obfuscated download cradle, or hidden-window .NET.
  • Application whitelisting (AppLocker / Windows Defender Application Control) – forbids unsigned EXE from %TEMP%.
  • E-mail gateway: strip ISO, IMG, VHD, OneNote, JS and auto-disable macro-by-default for Office.
  • Regular offline backup (3-2-1) + immutable cloud snapshots (object lock / “legal hold”).

2. Removal – Incident Response Workflow

  1. Disconnect affected machine(s) from network (both Ethernet & Wi-Fi).
  2. Collect volatile evidence (MFT, Prefetch, ShimCache, Event-ID 4688) if forensics planned, then power-off.
  3. Boot from clean USB – use Windows PE / Linux IR distro → copy ransom note + sample (for ID) but do NOT mass-copy encrypted data.
  4. Re-image OS volume after backing-up encrypted user data externally. Zero-fill free space or full-disk NVMe secure-erase if time permits.
  5. Patch OS / 3rd-party apps fully; restore only after EDR or clean offline scan confirms baseline.
  6. Rotate every credential that existed pre-incident (especially RDP, domain, VPN).
  7. Re-import data from last known-good backup; if no backup, keep .fonix files for possible future decryptor.

Tip: Fonix no longer re-launches at boot, but always check HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run for "Default" = "C:\Users\Public\svchost.exe" or similar random name.

3. File Decryption & Recovery

  • Good news: FILES ARE DECRYPTABLE – the master private key was published 11-Jan-2021 by the Fonix author himself when he shut the RaaS.
  • Decryptor tools:
    – Official FonixDecryptor.exe (signed by “TVT” and released in GitLab & BleepingComputer).
    – Generic alternative: use “RansomwareFileDecryptor” from Emsisoft v1.0.0.7 which imported the leaked .pfx key pair.
  • Command-line example:
    FonixDecryptor.exe -d D:\Recover -p \\NAS\Encrypted -o D:\Decrypted -k master_privkey.pem
    Run as Administrator, disable AV heuristic temporarily (some vendors still flag decryptor as hack-tool).

Recovery feasibility notes:

  • Only versions prior to v4.1 (SHA-256 4d1b97…) are 100% covered. A handful of post-shutdown impostors changed the RSA key; those newer samples cannot be opened with the public tool—check hash first.
  • If you lost filenames & folder structure, the decryptor supports “keep-encrypted-originals” switch (-b) so you can diff/compare.
  • Expect roughly 150 GB/h on SATA SSD; network shares via SMB will be slower.

4. Other Critical Information

  • Unique traits:
    – Fonix was among the first to adopt .NET 5 cross-platform crypter stub, though Windows-only builds were delivered.
    – Affiliate revenue model used Telegram bot for “victim queue” (ID leaked in ransom note footer) – made tracking easy for researchers.
    – Once encryption ends, it shows a fake Windows Update screen (“Working on updates 0%”) for up to 30 min to delay user reaction.

  • Broader impact:
    – Most victims were small clinics, municipal governments, and universities in US, DE, TR, during 2020-21 winter COVID-19 staffing shortages.
    – Average demand 0.5 – 2 BTC; payment rate relatively low because free decryptor appeared only 7 weeks after campaign peak.
    – Campaign funded at least two follow-up threat-actors (Mespinoza/PYSA and BlackMatter affiliates) who hired the same RDP brute pool.

Stay safe, patch early, log PowerShell, and keep an offline backup—those three habits defeated Fonix in the field even before its master key leaked. Report any fresh .fonix sightings to your national CERT so we can confirm the sample’s key material is still covered by the public decryptor.