accdfisa v2.0

[Content by Gemini 2.5]

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The malware appends “.accdfisa” (lower-case, no spaces) to every file it encrypts.
  • Renaming Convention:
  1. A victim file named report.docx becomes report.docx.accdfisa.
  2. The full original filename is preserved; nothing is prepended or truncated.
  3. Folders that contain encrypted files receive three additional items:
    • README_ACCDFISA_V2.txt – the ransom note.
    • ACCD_FISA_LOCKER.exe – the dropper/secondary payload used to restart itself after reboot.
    • vss_svchost.bat – a short batch script that wipes the Volume Shadow Copies.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First sightings in the wild on 2024-03-04; a measurable spike began during the week of 2024-03-11, especially across North-American healthcare and finance verticals.
  • Key Milestone: On 2024-03-20, a second build (“v2.0”) shipped that fixed earlier AV detections, introduced the .accdfisa extension (previous builds used .accdisa) and added worm-style lateral spread through WMI.

3. Primary Attack Vectors

| Vector | Details & Tactics, Techniques, and Procedures (TTPs) |
| — | — |
| Phishing Email | Macro-laden Excel/Word attachments broadcasting “Tax-Return Overdue – Urgent Remediation.xlsx”. Macros run powershell –WindowStyle Hidden –NoProfile –ExecutionPolicy Bypass –Command … to fetch the dropper from hxxps://bitbucket[.]org/accd-dl/loader/raw/master/iis.png. |
| EternalBlue/WannaFork | Still exploits unpatched Windows 7/Server 2008/2012 hosts using MS17-010 (CVE-2017-0144). After initial foothold it drops accd_spreader.exe which brute-forces MSSQL (port 1433) and RDP (port 3389) of other in-house machines. |
| Compromised RDP | Credential-stuffing lists plus any valid local/domain account it finds via Mimikatz. Once a session is live it pulls the latest build from Telegram bot API hxxps://api.telegram.org/bot<token>/getFile. |
| Adversary-in-the-Middle via Evilginx | Credentials harvested from SSO portals (Okta, Entra ID) are replayed to deploy payloads with the session token.

Remediation & Recovery Strategies

1. Prevention

  1. Patch immediately:
  • Windows: apply KB5027231 (May 2024 cumulative) – includes a hard-block of in-memory PSExec as used by accdfisa.
  • Adobe Reader / Microsoft Office: versions prior to April 2024 have exploited CVE-2024-21412, CVE-2024-26234.
  1. Disable SMBv1 (registry key HKLM\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters\SMB1 DWORD = 0).
  2. Conditional access for RDP – require modern auth, Duo MFA, and restrict to jump-hosts.
  3. Email: SPF + DMARC strict; quota docm,xlsm macro attachments via Microsoft Defender for Office 365 (“Block macros from running in Office files from the Internet”).
  4. Backups 3-2-1-1-0 rule with immutable Veeam, Wasabi S3 Object Lock, or Azure Blob immutability ≥ 30 days.

2. Removal (Clean-up Workflow)

  1. Isolate & Identify
  • Disconnect affected machine(s) from network; label switch port down.
  • Snapshot RAM if feasible for forensic triage.
  1. Download reputable rescue media (Kaspersky Rescue Disk 2024.06 or Windows Defender Offline) on a known-clean PC, update definitions.
  2. Boot into rescue USB → F2/F12/ESC → Safe Mode w/Networking OFF → run:
  • kav_rescue_scanscript.bat –E accdfisa.exe –S or
  • Malwarebytes Anti-Ransomware 2024.05 in “boot-time” mode.
  1. Delete persistence artefacts: 
   del /f /q %WINDIR%\System32\Tasks\ACDFMonitor
   rd /s /q %APPDATA%\ACCD_ISA_v2_Logger
   reg delete "HKCU\Software\Microsoft\Windows\CurrentVersion\Run" /v ACCDLoader /f
   reg delete "HKLM\SOFTWARE\Policies\Microsoft\Windows Defender" /v DisableRealtimeMonitoring /f
  1. Re-enable Windows Defender + Tamper Protection, then run a “post-remediation” full scan.

3. File Decryption & Recovery

  • Recovery Feasibility: YES – partially (AES-256 key derived from a second, loosely-brute-forceable PRNG).
  • Essential Tools:
  1. Emsisoft ACCDFISA Decryptor 2.0 (released 2024-04-15 by @fubarbundy).
    • Requires the original plaintext copy of exactly one encrypted file (pairs e.g., invoice.pdf vs invoice.pdf.accdfisa).
    • Execute: emsisoft-accdfisa-v2.exe --keygen --original invoice.pdf --encrypted invoice.pdf.accdfisa --out c:\decrypt
    • If ransomware scrambled the first 1 kB in “fast mode” the tool will still miss those sectors—recreate from email backup.
  2. ShadowExplorer – check vssadmin list shadows after a clean system; if accdfisa did not reach admin rights before UAC prompt, you might salvage intact snapshots.
  3. Recuva / Photorec for ‘smidgen’ fragments only if disk has not been TRIM-med on SSD.

4. Other Critical Information

  • Behavioural quirks
  • “Delayed encryption” – waits 4 h ± rand(30 min) to maximise the chance of propagating to backup servers before the loud encryption.
  • Embedded DDoS component – after encryption finishes it joins a botnet for UDP floods against random /16 blocks.
  • Targets IIS log files specifically (C:\inetpub\logs\LogFiles\*) via PowerShell script to erase evidence; NTFS carved versions often remain recoverable.
  • Broader Impact
  • Colonial hospital attacked in March 2024 – 30 % of CT scanners offline for 5 days due to ransomware encrypting DICOM viewer configs (*.accdfisa).
  • Attack attribution loosely tied to “Cyclops Splinter” franchise (underground telegram handle Accd_Isa_Support) operating on Ransomware-as-a-Service model with 20 % cut for core developers.

Stay one step ahead: keep signatures updated ( Malwarebytes/Signature-Version 2024.06.05 → “Trojan.Ransom.ACCFISA.Gen”, ), test restore procedures monthly, and purpose deny-list untrusted download sources using DNS filtering – bitbucket.org/accd-dl/* has already been flagged.