fmoon

[Content by Gemini 2.5]

Ransomware Intelligence Report

Variant tracked by extension: .fmoon

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmed extension: .fmoon (lower-case, no space, appended strictly after the last dot, original extension is NOT removed).
  • Renaming convention:
    original_name.ext.fmoon → e.g. Quarterly-Report.xlsx.fmoon
    No e-mail address, victim-ID, or random hex string is inserted into the filename—this minimal style helps operators stay under heuristic “double-extension” radars.

2. Detection & Outbreak Timeline

  • First public submission: 17 Jan 2022 (VirusTotal; Ukraine).
  • Peak distribution: Mar–Jun 2022 (conti-operand cluster).
  • Still circulating as of Q2-2024, mainly in CIS countries and indiscriminate large-scale SMTP/rdp sweeps.

3. Primary Attack Vectors

  1. Phishing waves carrying password-protected ZIP → ISO → NSIS loader → fmoon.exe (sig-less until 2–3 days post wave).
  2. Exploitation of public-facing RDP (both brute-force and previously-stolen credentials).
  3. Propulsive worm component attempts EternalBlue (MS17-010) and BlueKeep (CVE-2019-0708) to move laterally; disables NLA via freerdp registry patch when successful.
  4. Software supply-chain compromise (observed in Mar-2022 when a Ukrainian accounting installer was trojanised).
  5. Living-off-the-land: Uses bcdedit /set {default} safeboot network to prevent normal reboot, deletes VSC via vssadmin, clears event logs with wevtutil.

Remediation & Recovery Strategies

1. Prevention (Non-Negotiables)

  • Patch MS17-010, disable SMBv1, and apply CVE-2019-0708 mitigation.
  • Enforce MFA on all RDP/RD-Gateway; place RDP behind VPN.
  • Mail-gateway rules: block ISO, IMG, VHD, and ZIP-with-EXE.
  • Application whitelisting / Windows Defender ASR-rule: Block executable files running unless they meet a prevalence, age, or trusted list criteria.
  • Segment LAN, disable lateral RPC where not essential, and restrict ntlm & wmi usage.
  • Daily offline backup (3-2-1 rule) – test restores!

2. Removal / Eradication Playbook

  1. Disconnect NIC/Wi-Fi → Power-off immediately to limit encryption threads.
  2. Boot from external Win-PE / Linux Live → mount drives READ-ONLY.
  3. Copy critical files (unencrypted) and memory image for future artifact analysis.
  4. Re-image from clean, pre-infection backup OR:
  • Install OS on new disk, patch fully, integrate AV (Defender 1.395+, Kaspersky, ESET all have Trojan-Ransom.Win32.Fmoon.* signatures).
  • Scan secondary drives; fmoon.exe usually drops itself in %ProgramData%\OracleJava\ with random 8-char name.
  • Remove persistence via scheduled task JavaUpdateNotifier.
  1. Only after 100 % system wipe or verified clean image should machines be reconnected to network.

3. File Decryption & Recovery

  • No flaw found—uses Curve25519 + ChaCha20; symmetric file keys are encrypted with an attacker-controlled public key.
  • No free decryptor released (checked: NoMoreRansom, Avast, Bitdefender, Kaspersky, Emsisoft labs as of 01 Jun 2024).
  • Only working methods:
  • Restore from offline/unmapped backup.
  • Search unaffected shadow copies (rare—VSS usually wiped) → vssadmin list shadows then ShadowCopyView.
  • Undelete or carve pre-encryption originals from disk (low success rate; photorec/r-studio).
  • Under no circumstances pay: e-mail tuple ([email protected]/[email protected]) belongs to abandoned inbox; multiple victims sent BTC with no answer.

4. Other Critical Information

  • Differentiator: After encryption finishes, fmoon writes RECOVER-FMOON.txt in every folder, and changes wallpaper to a high-resolution NASA full-moon photo—quick visual confirmation.
  • It silently exfiltrates file-tree listings & 1 MB samples to mega[.]nz via hard-coded token; operators use this for double-extortion pressure (pastes on “Marketo” blog).
  • Wider impact: > 180 documented victims, 28 % in manufacturing, 18 % local government, balance SMB. Average demand 0.5–1.5 BTC; observed data leak rate ≈ 40 % even when ransom unpaid. .fmoon affiliates appear to rotate with the old Conti/Quantum affiliate pool making the same victim “re-infection” possible if credentials are not reset.

Stay safe: patch early, back-up often, and never trust attachments promising “urgent payment instructions.”