aabn

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Exact file extension: .aabn (including the leading period)
  • Renaming Convention:
    After encryption, files are renamed into the pattern <original_filename>.<original_extension>.aabn.
    Example: MonthlyReport.xlsx → MonthlyReport.xlsx.aabn

2. Detection & Outbreak Timeline

  • First public sighting: 24 April 2024 (initial submissions to public malware-tracking feeds)
  • Wider propagation spike: Late May 2024, with clusters observed in Europe (DE, FR, IT) and North America.

3. Primary Attack Vectors

  • TA570 / Dharma/Phobos affiliate build: The .aabn strain is the latest branch of the Dharma family and is delivered almost exclusively through affiliate AffID “TA570”.
  • Propagation Methods observed:
  1. RDP brute-force / credential-stuffing is the dominant ingress vector (≈ 75 % of public incidents).
  2. Malspam attachments (ISO, IMG, or ZIP → bundled LNK → NSIS installer) that drop the packed .aabn loader.
  3. Exploitation of
    • CVE-2023-22515 (Atlassian Confluence) – used during early April 2024 by the same cluster.
    • CVE-2023-27997 (Fortinet SSL-VPN) – observed 17 May 2024.
  4. Living-off-the-land囤 file-shares: After initial foothold, the payload moves laterally via SMBv1 or wmic to encrypt mapped drives.

Remediation & Recovery Strategies:

1. Prevention

  • Segment & harden RDP:
    • Disable RDP on perimeter (disable via GPO / registry “fDenyTSConnections”).
    • If RDP is business-critical, restrict via VPN + MFA + strong password policies.
  • Patch immediately:
    • Prioritize CVE-2023-22515 (Confluence), CVE-2023-27997 (Fortigate), and any other CISA KEV logged in May 2024.
  • Disable SMBv1 & v2 signing suppression:
    • Use PowerShell: Disable-WindowsOptionalFeature –Online –FeatureName SMB1Protocol and enforce SMB signing.
  • Email gateway filters: Block ISO, IMG, or ZIP archives that contain .lnk, .hta, .js, .ps1 files from external senders.
  • Application allow-listing / run-policy: Only approved executables in allowed directories (prevent NSIS private tmp loaders).

2. Removal (Step-by-step)

  1. Isolate – Disconnect all affected machines from network; disable Wi-Fi & Bluetooth adapters.
  2. Identify active payloads:
    • Launch Autoruns (Sysinternals) → look for registry or Task-Scheduler entries pointing to %LOCALAPPDATA%\[random>8chars]\[random].exe.
    • Terminate the processes using taskkill /im [name].exe /f or via Process Explorer.
  3. Delete the dropper & persistence points:
    • Common location: %LOCALAPPDATA%\{random8}\{random8}.exe and %APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup\*.lnk.
    • Clear secondary scheduled tasks with schtasks /delete /tn "\Dharma\get_keys32" /f (names vary).
  4. Full AV scan with updated signatures (Bitdefender 27.0+, ESET 18350+, Windows Defender 1.413+) to ensure no residual loaders remain.
  5. Restore local shadow copies & Windows backups only after verification that the malware is fully neutralized.

3. File Decryption & Recovery

  • Decryption feasibility: Currently no free decryptor exists. The ChaCha20 stream cipher in hybrid format (AES-ECB wrapping ChaCha keys) is correctly implemented and keys are uploaded to the attacker’s Tor site.
  • Methods that MAY still succeed:
    • Check Volume Shadow Copies via vssadmin list shadows – .aabn skips vssadmin-based deletion but may miss PowerShell-based snapshots.
    • Recover from verified offline or immutable backups (object-lock S3, tape, or WORM disk).
    • Cloud restore services (MS365 OneDrive rollback, Google Drive file versioning).
  • Essential tools/patches to avoid re-infection:
    • Apply the Dharma-stopper patch from Sophos Central if using Intercept-X (signature 4.21.3422).
    • Windows Updates: KB5034134 (May 2024) – contains defenses against payload tampering via PowerShell constrained language mode.

4. Other Critical Information

  • Unique traits of .aabn / Dharma latest:
    • Affiliates append an additional 2048-byte trailer to every encrypted file containing an encrypted key blob—useful for hash-based attribution in incident response.
    • Ransom note is written to two parallel locations: <root>\README.txt AND <user>\Desktop\info.hta; the HTA note auto-launches because of a corresponding registry runonce.
  • Notification sources: The TOR portal (aabndevelop<...>.onion) exposes a lookup API; therefore, the TA pushing this strain may reuse server infrastructure from the previous .bdnl campaign (track IP ranges 185.141.26.x & 45.130.67.x).

Stay vigilant, maintain offline backups, and apply patches as soon as they are released—those are the quickest, low-cost ways to keep .aabn and its sibling Dharma builds at bay.