fantom

[Content by Gemini 2.5]

Fantom Ransomware – Community Resource

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmed extension: .fantom
  • Renaming convention:
    [original_name].[original_ext].fantom (i.e., the malware simply appends “.fantom” to every file – nothing is stripped away, so Invoice.xlsx becomes Invoice.xlsx.fantom).
    Supplementary mark: the ransom note is written into DECRYPT_YOUR_FILES.html and DECRYPT_YOUR_FILES.txt in every traversed directory.

2. Detection & Outbreak Timeline

  • Earliest public sightings: 1-st half 2016 (Juniper Threat Labs first blogged it 9 Jun 2016).
  • Mini-resurgences observed: until late 2016; most families seen today are old dormant builds that wake up after lateral movement inside stale networks – not new campaigns.

3. Primary Attack Vectors

  • Spear-phishing e-mails carrying “.exe” or “.scr” that masquerade as “critical Windows update” or “fax document”.
  • Exploit-kit secondary drops: once Angler/Elderwood EK compromised a browser, Fantom was pushed as final payload.
  • RDP brute-force → interactive install by human operator (post-2016 incident data).
  • No SMB/“worm” component (differs from contemporaries such as Zepto or SamSam) – relies purely on the above vectors and subsequent manual pivoting.

Remediation & Recovery Strategies

1. Prevention

  • Patch OS + 3rd-party apps (Fantom’s dropper used the old .HTA CVE-2016-0189 in IE and the 2012 CPL/PIF tricks).
  • Remove local-admin rights from day-to-day accounts and enforce AppLocker/Windows-SRP: %TEMP%\*.exe → block.
  • Restrict RDP: move from 3389, enforce 2FA/VPN-only, set “Account lockout” for failed logins.
  • Mail-gateway: strip *.exe, *.scr, *.pif; sandbox attachment detonation.
  • Maintain offline, password-protected backups (3-2-1 rule) before the first suspicious file appears.

2. Removal

  1. Disconnect from network (Wi-Fi/ethernet) immediately.
  2. Boot into Safe Mode with Networking.
  3. Run a reputable AV/EDR boot-scan (Kaspersky AV-Tool, Sophos Scan-&-Clean, MS Defender Offline) – they all detect Fantom as:
  • Ransom:Win32/Fantom.A
  • Trojan-Ransom.Win32.Fantom.*
  1. Remove persistence:
  • Registry Run key → HKCU\Software\Microsoft\Windows\CurrentVersion\Run\“Windows Update” → %TEMP%\windows-update.exe
  • Scheduled task WindCom_Updater (XML droppers love Task Scheduler).
  1. Delete the ransom notes (DECRYPT_YOUR_FILES.*) manually – they are not harmful but clutter restore attempts.
  2. Reboot normally; confirm no new .fantom files appear during a 30-min idle period.

3. File Decryption & Recovery

  • Decryptable? YES – Fantom uses a LOCAL 128-bit AES key that is itself encrypted with a static embedded 1024-bit RSA public key. The private half was recovered and published by CERT-BR on 20 Dec 2016.
  • Tool: Fantom_Decryptor.exe (“FantomDecrypter” – available from Emsisoft, BleepingComputer, NoMoreRansom).
    Operation:
  1. Copy tool onto clean machine or an isolated VM that mounts the infected drive as read-only.
  2. Run FantomDecrypter.exe → “Scan entire system”.
  3. Tool automatically renames *.fantom back → original extension and AES-decrypts in-place.
  4. When finished, validate a few random documents before deleting the .fantom copies.
  • No guarantee on modified variants: if the operator replaced the embedded RSA key (happened twice in 2017 sub-campaigns), decryption is impossible without that private key – in that case, restore only from backups.

4. Other Critical Information

  • Fake Windows-Update GUI: While encrypting, Fantom pops up a full-screen gray dialog that looks exactly like the genuine Windows 10 “Installing update 37% – do not turn off your PC.” Users think the PC is patching; meanwhile encryption proceeds in the background.
  • Kill-switch check: Binary queries http[s]://guru3[.]com/sys/test.html (C2). Blocking the domain doesn’t stop encryption but prevents key upload – useful for forensics to ensure the local AES key is still present (needed for the free decryptor).
  • Extension collision warnings: Some unrelated wipers have copied the “.fantom” extension but are not AES+RSA and therefore NOT repairable with the public decryptor – verify ransom-note wording matches “DECRYPTYOURFILES.html” and VeraCrypt-style partition header is untouched.

Broader Impact

Fantom never reached NotPetya/WannaCry scale, but its fake-update social-engineering trick has since been reused by later families (Fonix, DarkSide, FakeWindows10). The wide availability of the RSA private key makes it a textbook example of why backups + responsible disclosure work: once researchers cracked the single key, virtually every victim worldwide could recover at zero cost – underscoring that a single mis-step by an attacker (re-using one RSA pair) can annihilate their business model.

Stay patched, stay backed-up, and keep the Fantom decryptor in your incident-response kit. Good luck and safe computing!