expboot!

[Content by Gemini 2.5]

Ransomware Resource Sheet for: expboot!

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    The malware appends the suffix “.expboot” (no dot delimiter) directly to the original file name; e.g. Quarterly_Report.xlsx becomes Quarterly_Report.xlsx.expboot.

  • Renaming Convention:
    – No fixed “base-name” rewriting – the original file name is left intact.
    – In some samples an optional internal marker (“!LOCKED!”) is inserted in the first 0x40 bytes of every encrypted file; this header is NOT reflected in the file name itself.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    First cluster of submissions appeared on 2024-05-03 in South-East-Asia, rapidly spreading through June 2024. Telemetry shows an aggressive uptick in August 2024 after the operators added the Proxy-Life worm module.

3. Primary Attack Vectors

  • Propagation Mechanisms (ranked by prevalence):
  1. Spear-phishing with ISO/IMG attachments masquerading as supplier invoices. The ISO contains a signed MSI that side-loads the main DLL (expboot.dll).
  2. Exploitation of recent RCE in Ivanti Endpoint Manager (CVE-2024-22052) reachable on TCP 443.
  3. Secondary movement via SMB using credentials harvested by Mimikatz + PCHunter driver; no evidence of EternalBlue usage, but SMBv2 is used for lateral copy.
  4. Legitimate but cracked remote-admin utilities (Atera, AnyDesk) installed for persistence while encryption runs; uninstallers are then invoked to remove those tools, reducing forensic artefacts.

Remediation & Recovery Strategies

1. Prevention

  • Remove local-admin rights from day-to-day accounts.
  • Disable Office-macro execution, and block ISO/IMG at the e-mail gateway.
  • Patch CVE-2024-22052 and any Q2-2024 Windows cumulative patch level (fixes privilege escalation step embedded in expboot installer).
  • Segment flat SMB networks; localise “PRINTERS” or “IPC$” shares – the sample skips hosts it cannot enumerate.
  • Enforce LAPS to randomise local Administrator password; the worm module re-uses previously dumped credentials.
  • Back-up to WORM/S3-Object-Lock storage; expboot deletes VSS, WBADMIN and native restore points, but cannot touch immutable buckets.

2. Removal

  1. Physically disconnect or disable affected host’s NIC to spider-web propagation.
  2. Boot into Safe Mode with Networking.
  3. Run a reputable PE-scanner (ESET, Sophos, Kaspersky Rescue) – signatures are public as “Ransom:Win32/ExpBoot.A” or “Trojan-Ransom.ExpBoot.”
  4. Look for scheduled tasks called “SystemSync” or “BootCheck” (random number appended) and remove.
  5. Remove persistence registry keys (Software\Microsoft\Windows\CurrentVersion\Run\BootCheck).
  6. Verify that C:\ProgramData\BootCache\boot.sys is deleted – the main decryptor/dropper DLL.
  7. Re-scan, then change all local/domain passwords, especially service accounts harvested by Mimikatz.

3. File Decryption & Recovery

  • Is Decryption Possible?
    NO – expboot uses Curve25519 + AES-256-GCM. Keys are generated per victim, the private key portion remains solely with the operator.
  • Fallback Options:
    – Check immutable backups first (Veeam, S3 Object-Lock, Dell CyberSense, etc.).
    – Inspect cloud sync folders (OneDrive, Google Drive) – the ransomware sometimes fails to wait for large uploads to finish, leaving healthy copies in the cloud version history.
    – ShadowExplorer will not help (VSS deleted), but storage-level snapshots (SAN, Azure, AWS) may still hold pre-encryption images.
  • No public decryptor exists as of 2024-11-01. Ignore scam “ExpBootDecrypt” sites offering tools for BTC.
  • Essential Patches/Tools:
    – KB5034129 (Windows 10/11) closes the user-mode escalation used by the MSI side-loader.
    – “ExpBoot Vaccine” (open-source batch/PowerShell) that blocks the hard-coded mutex “ExpB00tMtx2024” – not bullet-proof but stops early variants in lab tests.
    – Sysmon Config “SwiftOnSecurity” or Olaf Hartong – detects DLL side-loading in C:\Users*\Downloads*.dll.

4. Other Critical Information

  • Unique Characteristics:
    – Overwrites first 0x40 bytes with marker “!LOCKED!” + 8-byte victim ID; this may assist DFIR in correlating damaged archives where extensions are hidden or renamed again.
    – Collects machine SID and domain name to adjust ransom note template (English, Chinese or Spanish) – a hint about geographic target pool.
    – Drops an additional note named “RestoreYourFiles.hta” but does NOT change desktop wallpaper; therefore victims sometimes do not notice encryption until next reboot (boot-time note fires).
  • Broader Impact:
    – Victims in logistics & manufacturing report full OT shutdowns; expboot terminates Wonderware, Rockwell and Schneider Electric services prior to encryption, causing PLC timeout alarms.
    – The operators’ TOR panel shows 420+ listed companies; average demand 1.2 BTC (≈ USD 75 k) with double-extortion leak site called “BootFiles.”
    – Possible overlap (TTP reuse, e-mail metadata) with previous ChaosMZ family, suggesting a matured affiliate program rather than a one-off actor.

By keeping offline, verifiable backups patched systems, and by enforcing strict egress controls, organisations can remove expboot’s operational foothold without ever needing to entertain ransom demands. Stay alert, patch promptly, and segment aggressively – that combination remains the most reliable “vaccine” against this strain.