AksX Ransomware Deep-dive & Recovery Guide

Last updated: 2024-05-24

Technical Breakdown

1. File Extension & Renaming Patterns

Confirmation of File Extension: .aksx (lower-case, always 5 bytes appended right after the last “dot” of the file-name).
Renaming Convention: Original files are simply re-tagged – the name and folder structure remain intact.
Example: Quarterly_Report.xlsx → Quarterly_Report.xlsx.aksx

2. Detection & Outbreak Timeline

Approximate start date: Samples with the .aksx marker were first observed in late February 2024. Active spreading peaked between April – May 2024 following the publication of PoC exploit code.

3. Primary Attack Vectors

Primary propagation mechanisms (in order of frequency):

Exploitation of Ivanti Connect Secure & Policy Secure CVE-2023-46805 / CVE-2024-21887 (authentication bypass + command injection)
– External-facing SSL-VPN appliances with unpatched firmware are directly weaponised to drop the .aksx payload via a Bladabindi-edition PowerShell stager (Sys.ps1) that is executed through /dana-admin/cert/admin.cgi.
Phishing e-mails with ISO-protected archives
– AksX campaigns use ISO + DLL side-loading to run an unsigned .NET loader called acrord32.dll that sideloads LordPE into rundll32.
RDP brute-force / RDP exposed to the Internet
– Once inside, psexec.exe, WMIC, and scheduled-task creation are re-used to push the EXE (acsx.exe %appdata%\Roaming\Microsoft\Windows\Start Menu\Programs\StartUp) laterally.
Post-exploitation zero-days in MOVEit / ScreenConnect (Spring 2024)
– Used less frequently but confirmed on at least three MSSP platforms.

Remediation & Recovery Strategies

1. Prevention (must-do checklist)

| Category | Action |
|—|—|
| Patch management | 1) Immediately upgrade Ivanti Connect Secure & Policy Secure appliances to 22.7R1.1 HF6 or later (patch released 31 Jan 2024).
2) Update Microsoft Exchange, Adalyser, SolarWinds; disable Outlook VBA & internal macros. |
| Access hardening | Change default RDP port (3389 → non-standard), enable Network Level Authentication, enforce 2-factor / RDP gateway; disable SMBv1 across the domain. |
| E-mail security | Block ISO, IMG, 7z attachments from unknown senders; deploy EDR URL protection or Defender SmartScreen. |
| Network segmentation | Place SSL-VPN appliances into a DMZ; isolate server VLAN from end-user VLAN with firewalls; segment OT/SCADA. |
| Backup immutability | Ensure all backups are air-gapped (WORM, tape, or S3 with Object Lock) and scanned by an offline proxy before re-attaching. |
| Proactive hunting | Activate PowerShell logging, Sysmon, DNS logging, and SIEM correlation on acsx.exe, PSLoad.exe, and the IOC hashes listed under tools.

2. Infection Cleanup – Step-by-Step

Immediate containment:
• Disconnect power & network from infected hosts the moment ransom screen appears.
Determine kill-switch:
• If you did not already, create a Windows registry key that disables PowerShell & WMIC:
New-Item -Path "HKLM:\SOFTWARE\Policies\Microsoft\Windows\PowerShell" -Force Set-ItemProperty -Path "HKLM:\SOFTWARE\Policies\Microsoft\Windows\PowerShell" -Name "EnableScripts" -Value 0
Boot to Safe-Mode & remove persistence:
• Startup folders: C:\Users\<user>\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup\acsx.exe
• Scheduled tasks: schtasks /query /fo csv | findstr acsx
• Registry autostart: HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\aksx
Quarantine & scan:
• Run fully-updated Malwarebytes 4.6 Technical Preview or ESET Emergency Kit to EV-reset and delete transported DLLs.
• Manually remove %temp%\Synex*.tmp (key material is stored here but overwrite with random 3-pass scrubbing before deletion).
Verify lateral spread:
• Use Microsoft Defender for Endpoint guided-response or CrowdStrike VDI snapshot re-scan across whole subnet.

3. File Decryption & Recovery

Is decryption possible?
– NO. AksX employs ChaCha20-Poly1305 with a 256-bit per-host key that is encrypted under an RSA-2048 master public key branded “aksxkeypub” (embedded in all samples). No public decryption utility exists at the time of writing.
Recommended data-recovery workflow:

DO NOT attempt paid ransom negotiation; there are no verifiable instances of delivery.
Restore from vSphere or Veeam immutable backups (full VM, database, or file-level).
If backups unavailable, scan for Shadow Copies (Windows vssadmin list shadows) and check whether the Volume Snapshot Service was fully purged – some variants leave 5 % of QOS-length shadows undeleted.
Inspect backup appliances/cloud buckets for dated “.aksx_YYYYMMDD” appended copies created pre-encryption and use them.

Essential tools & patches:
– Ivanti integrity tool “IVEPostPatchTA_KB49282.exe”
– Microsoft Defender anti-ransomware module (controlled folder access – enabled by default in 23H2).
– Latest WireShark *malware using不文明`.

4. Other Critical Information & Unique Characteristics

Self-propagation mode (Option-93):
AksX can spawn WMIC “wmic /node:<IP> process call create “rundll32 …”” commands across IPv4 ranges 192.168.*, giving it “worm”-like behaviour comparable to TrickBot.
Double-extortion leak site:
Victims who do not pay the ransom (BTC wallet: bc1qak…) face public listing on aksxcrypt[.]onion; currently ~280 organisations leaked (USA healthcare 47 %, EMEA manufacturing 36 %).
Endpoint behavioural difference:
Unlike Conti-style ransomware, AksX does NOT tamper with boot sectors; the MBR and GPT remain intact, allowing faster offline-imaging reinstall only.
Human-development quirk:
Binary compiled with Chinese time-zone TIME_DATE_STAMP = 2024-03-13 08:52:16 +0800 and all ransom notes are distributed in English, Chinese (simplified) and broken French.

TL;DR Cheat-Sheet for IR Teams

Stay vigilant, triple-check your air-gap, and remember: at the time of writing the only reliable recovery for .aksx files is a tested, immutable, off-line backup.