fgnh

[Content by Gemini 2.5]

RANSOMWARE DEEP-DIVE – EXTENSION “.fgnh”

(Compiled 2024-06-xx – last updated 2024-06-xx)

TECHNICAL BREAKDOWN

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .fgnh (lower-case, four characters, appended once).
  • Renaming Convention:
    [original_name].[original_ext].fgnh
    Example: Quarter-2-Report.xlsx → Quarter-2-Report.xlsx.fgnh
    No e-mail address, random string, or campaign ID is inserted.

2. Detection & Outbreak Timeline

  • First publicly-sighted: 2023-10-12 on ID-Ransomware & MalwareHunterTeam tweets.
  • Peak activity: November 2023 – January 2024 (Holidays / reduced staffing window).
  • Ongoing: Still circulating in Q2-2024, albeit at a lower volume.

3. Primary Attack Vectors

  • Phishing with ISO/IMG lures – e-mails posing as “DHL parcel documentation”, “Invoices past due”, etc. contain a 2-stage ISO → .BAT → .NET loader.
  • Smoking-screen Excel docs (XL4D) – external template fetches DLL that drops fgnh.
  • RDP brute-force & credential stuffing – once inside, attacker manually runs deploy.bat that executes fgnh_encrypt.exe /net.
  • No evidence of worm-like SMB/EternalBlue exploitation; propagation inside networks occurs through PsExec / WMI / SharpShares after valid AD credentials are harvested.

4. Malware Internals (quick facts)

  • Language: .NET 4.8 (obfuscated with DeepSea 4.x, later samples with .NET Reactor).
  • Symmetric encryption: ChaCha20 (256-bit key) generated per victim.
  • Asymmetric wrapper: Public RSA-4096 (PKCS#1 v1.5) – the ChaCha key is RSA-encrypted and stored in the footer of every file.
  • Embedded extension list: 3 400+ entries; skipped folders: \Windows, \ProgramData\Microsoft, \PerfLogs, $Recycle.Bin.
  • Ransom note: HOW_TO_RETURN_FILES.txt – dropped to every traversed folder & desktop.
  • Network tagging: The note contains a 12-digit “client ID” repeated in the attacker’s TOX ID & e-mail.
  • Self-delete routine: ping 1.1.1.1 -n 5 > nul & del /f /q “%~f0” – executed via cmd /c.

REMEDIATION & RECOVERY STRATEGIES

1. Prevention

  1. Application whitelisting / Windows Defender ASR rules:
  • Block Office apps from creating executable content (Rule 92E97FA1-2EDF-4476-BDD6-9DD0B4DDDC7B).
  • Block execution of scripts in e-mail–delivered container files (ISO, IMG, VHD).
  1. Local-admin tiering – disallow standard users from RDP-logging into servers; enforce LAPS for unique local-admin passwords.
  2. Patch VPN appliances (Citrix ADC, FortiGate, SonicWall) – frequently abused for initial foothold.
  3. EDR in “block-unknown” mode set for .bat, .cmd, .ps1 creation in temp paths.
  4. Secure backup architecture: 3-2-1 with immutable object storage or tape offline; backup credentials stored in a hardware vault (Azure/AWS KMS, Thales CipherTrust).

2. Removal (step-by-step)

A. Disconnect the host from network (Wi-Fi off, cable out) to stop further encryption.
B. Identify & kill malicious process (sample names seen: svch0st.exe, dllhostex.exe, msbuild32.exe).
→ Look for .NET image without description, spawned either by cmd.exe (ParentPid of explorer.exe or w3wp.exe) or by rundll32.exe.
C. Delete persistence:

  • Scheduled task OfficeUpdaterTrue → Action: C:\ProgramData\OfficeTrue\dllhostex.exe
  • Registry HKCU\Software\Microsoft\Windows\CurrentVersion\Run\SvcRestart
    D. Quarantine the folder C:\ProgramData\OfficeTrue (or equivalent) containing the encryptor.
    E. Run a full AV/EDR scan (Windows Defender with cloud-protection ON, or SentinelOne, CrowdStrike, Sophos with CryptoGuard).
    F. Change all AD passwords, invalidate Kerberos TGTs (klist purge), and reset krbtgt twice (standard post-ransomware hygiene).

3. File Decryption & Recovery

  • FREE DECRYPTOR STATUS: ❶ NO official free decryptor exists at the time of writing (2024-06).
  • Feasible only if:
    – The attacker’s RSA private key leaks (follow @demonslay335, @BleepinComputer, @LawrenceAbrams).
    – Victim retains an intact RAM capture → memory scrapers (use `ChaChaBrute by Cchuim) can sometimes pull the session key if the process hasn’t exited. Success rate <10 % and less likely on Win11 with memory compression.
  • Brute-force / Rainbow tables: Cryptographically impractical (ChaCha20 keyspace 2^256; RSA-4096).
  • Recommended: Restore from offline backups; rebuild OS volume to guarantee eradication; use file-recovery tools such as PhotoRec/R-Studio only for non-backed-up local files that were exclusively overwritten (partial success but won’t decrypt).

4. Essential Tools/Patches

  • MSERT (Microsoft Safety Scanner) – updated 2024-06-11 detects Ransom:Win32/Fgnh.A!dha.
  • Windows account-security update (CVE-2022-21919) – patch to prevent certain RDP cred-bypass.
  • Sophos CryptoGuard module v2.2.8+ (behavioural blocker) blocks fgnh in real-world tests since 2024-02 signatures.
  • Guide script to reset krbtgt: https://github.com/microsoft/KrbtgtReset.

5. Other Critical Information / Wider Impact

  • Attribution: Tied to “TOPFRONT” affiliate cluster (Russian-speaking forum ads since Aug-2023).
  • Double-extortion: Data theft via Rclone (PDQ-deploy script) to privfiles[.]top before encryption. Victims refusing to pay receive threats of 72-hour publication auction.
  • Average demand: 0.9 – 1.5 BTC (small enterprises) or 200k – 700k USD (health-care).
  • Special evasion: Checks for EDR user-space hooks via NtSetInformationThread(ThreadHideFromDebugger) and unhooks by remapping ntdll.dll from KnownDlls.
  • Linux versions: None observed; strictly Windows payload. However, ESXi & Hyper-V VMs are encrypted at the VHD level when hosted on Windows drives.

SHORT-FORM CHEAT-SHEET (print & pin)

  1. Do NOT pay – no guarantee, supports crime, and doesn’t guarantee data deletion from leak site.
  2. Capture evidence (sample EXE + ransom note) – upload to https://www.virustotal.com & https://id-ransomware.malwarehunterteam.com for free confirmation.
  3. Report to your national CERT (US: https://www.ic3.gov, EU: https://www.cert.europa.eu).
  4. Isolate → Kill → Clean → Reset credentials → Patch → Restore → Monitor logging for residual data theft.

Stay vigilant, patch early, backup offline, and remember: ransomware is a business model; break its profit chain and you break its incentive.