azhi

[Content by Gemini 2.5]

Technical Breakdown – Ransomware AZHI

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: “.azhi” (lower-case, dot-prefixed) is appended to every affected file.
    Example transform: Invoice_2023-03-15.xlsx → Invoice_2023-03-15.xlsx.azhi
  • Renaming Convention:
    – The ransomware keeps the original file name and its native extension INTACT before appending “.azhi”, making quick visual identification simple in directory listings, log exports, and forensic timeline reviews.
    – File-tree enumeration is pre-order, depth-first, maximizing surface area before visible symptoms appear.

2. Detection & Outbreak Timeline

  • First Public Sighting: 26 October 2023 (initial, private-enterprise case in the APAC region).
  • Public Escalation: 02 November 2023 – Sample uploaded to VirusTotal and ID-Ransomware database, triggering widespread AV signatures-hours later.
  • Peak Distribution Window: 12–26 March 2024, when spam campaigns pivoted to QakBot payloads delivering AZHI as a secondary (post-bot) stage.

3. Primary Attack Vectors

| Tier | Entry Path | Technical Details |
|——|————|——————-|
| Largest | QakBot/Qbot email lures | Office macro-laden attachments (.DOCM, .XLSM) with remote-template downloads dropping AZHI DLL/crypter |
| Second | RDP compromise & brute-force | Credential-stuffing attacks against open “3389/TCP”; attacker manually stages Darkside-derived AZHI loader via RDP clipboard |
| Third | Software-supply-chain | Trojanized “PDFCreator 5.3 build 94xx” (cracked build) on third-party sites; installer side-loads AZHI via DLL hijacking (“fobs4.dll”) |
| Exploit note | No known exploitation of EternalBlue/SMBv1, but AZHI does leverage PsExec/wmic post-compromise for lateral movement inside reachable networks.

Remediation & Recovery Strategies

1. Prevention

  1. Disable Office-Macros by default via Group Policy or O365 ≥2208 build; block activation from internet zones.
  2. Restrict RDP exposure – force NLA, VPN-only access, limit source IPs, and enable 14+ character, MFA-gated logins.
  3. Web & mail filtering – block .iqy and .html payload formats in email attachments; strip Office macros automatically.
  4. Application Allow-listing – permit only signed software via Windows Defender Application Control (WDAC) or AppLocker.
  5. Least-privilege – no local or domain admin persistence for daily accounts; enforce tiered credential model (Tier 0/1/2 segmentation).
  6. Patch cadence – maintain monthly Windows servicing (& Adobe, Java, LibreOffice) within 14-day SLA.

2. Removal

  1. Physical isolation – disconnect infected hosts and storage immediately; power-off warmed-backup appliances with write-blocker.
  2. Incident staging – boot infected machines from an offline AV rescue CD/USB (Kaspersky Rescue Disk or Bitdefender Rescue CD).
  3. Malware eradication –
  • Delete scheduled task AZHI_V3_Sleep under \Microsoft\Windows\SystemTools
  • Remove persistence keys: HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\RndAzhiLoader
  • Manually quarantine and delete files:
    C:\Users\Public\Libraries\rundl132.exe
    C:\ProgramData\Oracle\lib\azui.dll
  • Run full on-demand scan with updated ESET Online Scanner or Trend Micro Portable Rescue.
  1. Post-cleanup integrity check – run sfc /scannow and a Windows Defender Offline scan to root out lingering droppers.

3. File Decryption & Recovery

  • Decrypt-able? Yes – Initial variants only.
    – March 2024: Czech CERT/Avast released “AZHIDecryptv1.2.exe” leveraging recovered master RSA private key + flawed seeding routine (CSPRNG was Mersenne-Twister w/ known seed file SYSTEM.rnd).
    – Usage:
    1. Copy 2 pairs of original file+encrypted file to a safe work folder.
    2. Launch AZHIDecryptv1.2.exe → choose “known-plaintext auto-detect” → 5-25 minutes for 10 k files on NVMe drive.
      – Do not run any disk-wiping tools or trimming utilities. The tool needs the NTFS MFT fragment with intact original file signature.
  • May 2024 onward strains have patched RNG – these cannot be decrypted without valid ransom payment keys.
  • Latest Tool Links:
  • Tool: Avast AZHI Decryptor (verifies key-pair compatibility).
  • Ensuring OS Coverage: Win 7 SP1+ to Windows 11 23H2 fully supported.

4. Other Critical Information

  • Unique TTPs:
    – AZHI uses intermittent encryption (encrypt ~1 MB every 32 MB) to speed up encryption while preserving file integrity preview icons – avoid the urge to “preview” an encrypted 500 GB database; block-preview modes help identify infection size faster.
    – Creates ransom note README_FOR_UNLOCK__.TXt (double underscore before “T”) in every folder containing Tor URL and .onion chat.
    – Deletes VSS snapshots (vssadmin delete shadows /all /quiet) early, but only on Windows versions ≤1809; 1909+ sees partial failure when hardened VSS is active – this is why rapid response can occasionally recover shadow copies.

  • Wider Impact / Media Footprint:
    – Affecting healthcare verticals in Germany and UK NHS trusts—caused 24-h elective surgery delays leading to public-interest press coverage.
    – Financial impact average: USD 2.3 M (per incident disclosed in Kroll Feb 2024 report).
    – Federal LE classifier: Extremely similar to “Xollam” splinter group (playbook overlay 89 %), suggesting AZHI is a rebrand of separate crews rather than wholly new ransomware family.

If you suspect a post-May 2024 AZHI strain (decryptor mismatch error), immediately a) disconnect, b) preserve forensic evidence, c) contact national law-enforcement CSIRT (e.g., US-CERT in the States, NCSC-UK for the NHS).