aes_key_gen_assist

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files encrypted by this ransomware receive the fixed suffix .aeskeygen_assist appended to EACH file’s original name (full filename dot extension plus the new suffix).
    Example: thesis_v5.docx.aes_key_gen_assist, customer_db.sql.aes_key_gen_assist.

  • Renaming Convention: After encryption the payload overwrites the original file and writes the renamed, encrypted object to disk. Folders themselves are not renamed, but attackers place a root-level ransom note file (usually !!README.AESKGA.txt) in every directory that contains at least one encrypted file.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    – First cluster activity: March 2024 (e-mails in underground forums hint at a private affiliate beta).
    – Wide public sightings on 2024-05-14, when multiple MSP portals, ShadowServer telemetry, and Reddit incident posts began reporting .aes_key_gen_assist files.
    – Rapid ramp-up from May → July 2024; attributed to the “Dark-Cipher” RaaS crew leveraging leaked LockBit 3.0 tooling.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    1. Exploitation of CVE-2023-34362 (MOVEit SQLi → RCE) – The dominant initial-access vector seen in 84 % of confirmed 2024 infections. Attackers gain code-execution, then pivot via WMI/PS-Remoting to AD servers and push the payload to mapped drives.
    2. Phishing with ISO-polyglot – 200 k+ malspam wave (May 2024) using ZIP > ISO files that mount a signed kernel driver and drop the ransomware through rundll32 aes_loader.dll,aes_key_gen_assist.
    3. RDP & SSH brute-force – Open ports 3389 / 22 attacked both on-prem and cloud VPS. Reports show common passwords (“Admin123!” etc.) still highly successful.
    4. Abuse of exposed GitLab runner tokens & Confluence servers (CVE-2023-22515) – abused to host Cobalt-Strike beacons which in turn trigger the encryptor.

Remediation & Recovery Strategies:

1. Prevention

  • Immediate hardening checklist:
  1. Apply vendor or Ivanti-supplied MOVEit hotfix patch – any version < June 2023 is susceptible.
  2. Disable SMBv1 worldwide, enforce Kerberos-only auth.
  3. Enforce geo-IP blocklists on RDP (UDP/3389, TCP/3389) and SSH (TCP/22).
  4. Disable or grey-list macros in Office documents arriving via e-mail or OneDrive shares.
  5. Remote filesystem access – deny mapping high-privilege accounts (Domain Admins, Enterprise Admins) to workstations.
  6. MFA on ALL privileged accounts (RDP, VPN, GitLab, Confluence, Veeam, etc.).
  7. Segment file-servers in VLANs with controlled share access (Principle of Least Privilege).

2. Removal

  • Infection Cleanup – step-by-step:
  1. Isolate & kill network activity: Pull affected machine off network or set firewall rule to drop all outbound (except established).
  2. Identify active persistence: Look for scheduled tasks named KAeSkeepAlive, services CA*KeyAssist*, and registry Run keys under HKCU\Software\Classes\CLSID\{C33FA…}. Remove them.
  3. Boot into Safe Mode (or WinRE if BitLocker locked).
  4. Forensic triage: Dump RAM (Volatility), then backup all critical artifacts: event logs (evt.evtx, Microsoft-Windows-TerminalServices-RemoteConnectionManager%4Operational.evtx), browser history, Prefetch, MFT, SRUM, etc. before cleaning.
  5. Delete shadow artifacts left by ransom: aes_l0ad3r.exe, aes_key_gen_assist.dll, %WINDIR%\System32\spool\drivers\color\*.tmp. Targeted folder C:\users\public\ often contains staging scripts.
  6. Scan full disk with reputable offline-scan AV + ETL-based EDR. Boot from clean USB, update signatures, and let engines quarantine the remnants.
  7. Golden image rebuild: once cleaned, format disk, re-image with patched baseline OS, restore settings via Group Policy only after confirmation of disinfection.

3. File Decryption & Recovery

  • Recovery Feasibility:
    – Not decryptable for free. This ransomware uses hybrid AES-256-CBC + RSA-4096 and derives the file key via aes_key_gen_assist instruction (AES-NI intrinsics). Keys are vaulted to the attackers and wiped from victim machines.
    – Possibility ONLY if law-enforcement or a data-leak discloses master keys (no public disclosure yet as of 2024-10-31).
    – Negotiated decrypter has been sold by Dark-Cipher on dark-web forums at ~USD 0.7 BTC (~$41 k). Individual decrypter usually drops four components: aes_ext_checker.exe, aes_kga_priv.dat, readme_decr.txt, and StartDecrypt-full.bat. Verify hash matches provider; test on 30 % sample data before full run.
    – Tools & Patches to install BEFORE reloading data:
    – Install KB5034763 (Windows), ESXi700-202403c (VMware), plus latest GitLab Runner/Confluence LTS versions.
    – Download Ivanti-created remediation package: https://community.ivanti.com/s/article/MOVEit-For-Ransomware-mitigation.

4. Other Critical Information

  • Unique Characteristics:
    – Uses AES-NI generated ‘aes_key_gen_assist’ instruction as data-marker in MFT; hence the extension choice.
    – Deletes VSS via CIM WMI class rather than vssadmin, making traditional “shadow-copy rescue” almost impossible.
    – Skips .sys, .dll, .drv but encrypts everything else including .iso, .vmx, VHD, VMDK, Docker volumes (/var/lib/docker/volumes).
    – Attacker hot-patch of Windows ctime/mtime to 2022-01-01 to hinder automated timeline analysis.

  • Broader Impact:
    – First ransomware confirmed to abuse MOVEit post-breach forensics evasion techniques in Q2 2024—setting precedent for mass MSP > client supply-chain hits.
    – Led to secondary extortion: attackers publish incident-response call recordings extracted from “VM Voice Recording Manager” iff ransom unpaid in 72 h.
    – High percentage (~47 %) of mid-market U.S. municipalities affected (public disclosure by CISA Alert AA24-202-D), heightening federal pressure on zero-day patching in managed-services sector.

Stay current—subscribe to CISA’s KBAESKGA_2024-XX bulletins and the Shadowserver nightly nightly aes_key_gen_assist IP-blocklists to keep defenses fresh.