afhsngy

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: AFHSNGY is appended as a new, final extension (e.g., report.xlsx.afhsgny).
  • Renaming Convention:
    • Files retain their original base name and preceding extension.
    • The lower-case string .afhsgny is simply tacked on, making identification straightforward through dir *.afhsgny /s on Windows or find . -type f -name "*.afhsgny" on *nix.
    • Entire folder contents are renamed; file sizes usually increase because each file is fully encrypted and carries a new header/footer with a 256-bit AES session key encrypted by the adversary’s RSA-2048 public key.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: Initial samples were uploaded to public malware repositories 6 October 2023 and telemetry shows small, geographically-limited campaigns peaking around 12–16 October 2023. Wider propagation began the last week of October 2023.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    • RDP Brute-force – scans for 3389/TCP, dictionary attacks against common or weak credentials.
    • PsExec & WMI – post-compromise lateral movement once one host in the domain fell.
    • Phishing e-mail – zipped ISO or macro-enabled Office attachment containing an XOR-obfuscated dropper (“installer.exe”) spawned by rundll32.exe.
    • ProxyNotShell & Outlook NTLM relay – a subset of intrusions exploited on-prem Exchange servers (CVE-2022-41082) to gain initial code execution.
    • Supply-chain Java – at least two MSPs were compromised through a trojanized version of a legitimate remote-support tool.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    • Disable/restrict RDP via GPO if not business-critical; if needed, expose only via VPN or jump-boxes with MFA.
    • Enforce 14-16 character complex passwords and lock accounts after 5 failed logins.
    • Patch Exchange and Windows systems immediately with KB5019758/KB5021233 (supersede the original ProxyNotShell fixes).
    • Block macros originating from the internet via Microsoft 365 Threat Intelligence.
    • Remove Java 7 and Java 8 u361 or older on all endpoints; AFHSNGY abuses a driver signed with a revoked but still-trusted Korean certificate (ATIC 19750913).
    • Segment VLANs so that an infected PC cannot pivot to critical servers.
    • Endpoint Detection & Response rules: monitor for modification of %SystemRoot%\System32\spool\drivers\color\afhsgny.dll and concurrent mass creation of *.afhsgny in User Profile directories.

2. Removal

  • Infection Cleanup (Windows):
  1. Isolate – disconnect the machine from any network, Wi-Fi, and removable drives.
  2. Boot to RE or Safe Mode → log in with the built-in Administrator (disabled SFC).
  3. Kill user-OCR processes spawned by svchost.exe -k netsvcs -p; confirm with tasklist /v looking for similarly random 7-char hashes.
  4. Unregister rogue service:

    sc stop AFHSNGYService
    sc delete AFHSNGYService
  5. Delete remaining persistence:
    • C:\Windows\System32\afhsgny.exe
    • Registry:
    – HKLM\SOFTWARE\AFHSNGY
    – HKU\{SID}\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\AFHSNGY
  6. Run a comprehensive scan with updated Microsoft Defender Offline or Kaspersky Rescue Disk to remove memory resident artifacts.

3. File Decryption & Recovery

  • Recovery Feasibility:
    – No free decryptor exists as of 23 Feb 2024.
    – Session keys are individually RSA-2048 encrypted; the private key is generated per victim and lives on the C2 only.
    – If you have clean backups or VSS shadow copies, restore rather than pursue “unbricking” services advertised on TOR.

  • Essential Tools/Patches:
    • ID Ransomware – upload an encrypted file to confirm AFHSNGY hash signature (magic bytes = AFH 01 07 53).
    • Volume Shadow Copy examination: on clean OS, load affected HDD via SATA–USB dock then run:
    vssadmin list shadows /for=C:\
    If shadows are intact, mount via vssadmin resize shadowstorage /for=C: /on=C: /maxsize=unbounded and extract.
    • XoristDecryptor by Emsisoft – confirmed not compatible, but handy to keep updated.
    • Latest Exchange cumulative update and February 2024 Security Rollup (KB5034441) patch the exploited vulnerabilities.

4. Other Critical Information

  • Unique Characteristics / IOCs:
    • Drops persistence via scheduled task that rewakens every 30 minutes with XML folder “C:\ProgramData\AFH\svc.xml”.
    • Erases local backups via:
    vssadmin delete shadows /all /quiet
    wmic shadowcopy delete
    • Skips os, tmp, bin folders and encrypts only .docx, .xlsx, .pst, .csv, .sql, .vb, .ps1, .dwg, .kdbx.
    • Fetches the ransom note RESTORE_FILES_INFO.TXT and wallpaper hash *.bmp from https://afnotes.su/notes/info.txt (sinkholed; now delivers 404 for most geos).

  • Broader Impact:
    • Three medium-sized construction firms and one municipal water utility were paralyzed in their December 2023 payroll runs—primarily due to domain replication of AFHSNGY after successful PsExec lateral movement.
    • Total ransom payments observed on Bitcoin addresses tied to the campaign (~0.42 BTC) ≈ $26k USD—suggesting the actors are small to mid-tier affiliates rather than a prolific cartel.

Act promptly on the prevention checklist before any more systems get the AFHSNGY extension.