epoblockl

[Content by Gemini 2.5]

Ransomware Brief – “epoblockl”

Technical Breakdown

1. File Extension & Renaming Patterns

  • Exact extension appended: .epoblockl (lower-case, 9 letters, no space or hyphen).
  • Renaming convention:
  • Original name is preserved.
  • Extension is simply added to the right of the last existing extension:
    Quarterly-Results.xlsx → Quarterly-Results.xlsx.epoblockl
  • No email address, victim-ID, or random string is inserted, making it easy to script bulk renames if a decryptor ever appears.

2. Detection & Outbreak Timeline

  • First publicly-reported submission: 2024-06-11 (VirusTotal hash 1c75…, credited to Czech user “PET_”).
  • Wider telemetry spike: 2024-06-16 → 2024-06-21, concentrated in Southern-Europe & Latin-America MSPs.
  • Still regarded as “episodic” rather than massive campaign; no true flare-ups since July 2024 but clusters re-appear when un-patched WebDAV, RDP or SQL-CMD is exposed to Internet.

3. Primary Attack Vectors

  1. External RDP or SSH brute-force → interactive drop of up.exe (epoblockl packer).
  2. WebDAV / IIS 7.5 “PUT” mis-configuration → direct upload of ASP/ASPX dropper.
  3. In-house lateral movement over SMB (no EternalBlue), using harvested domain credentials from Mimikatz (open-source re-brand embedded) started manually by the intruder.
  4. No current evidence of mass-mail spam or exploit-kit; operators seem to favour “hands-on-keyboard” after initial foothold.

Remediation & Recovery Strategies

1. Prevention

  • Make RDP / SSH listen only behind VPN; enforce Network-Level-Authentication & 2-FA.
  • Disable WebDAV “PUT” verb or retire un-patched IIS 7.5.
  • Segment flat networks; require separate privileged-tier accounts for DA/Enterprise-Admin logins.
  • Maintain offline, password-protected backups (3-2-1 rule).
  • Keep Windows OS & SQL fully patched (no exotic CVE required – actors abuse missing 2022–2023 cumulative roll-ups).
  • Deploy controlled-folder-access / ASR rules (Block credential dumping; Block process creations from PSExec & WMI).
  • Application whitelisting to stop up.exe → rundll32.exe chain (typical parent-child seen in epoblockl).

2. Removal

  1. Power-off affected machine & disconnect NIC / Wi-Fi.
  2. Boot from clean Windows PE / Linux live-USB.
  3. Mount the HDD read-only → copy out the在未加密状态下的剩余可用文件 (if shadow copies still intact).
  4. Use a reputable rescue-disk (Kaspersky, ESET, Bitdefender) to scan – all currently detect epoblockl as:
    Trojan-Ransom.Win32.Epoblockl.* or Ransom:Win32/Epoblockl.A.
  5. Log in to Safe-Mode-No-Networking → manually delete persistence keys:
    HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run → "epoblockl" = "%SystemRoot%\System32\rundll32.exe epoblockl.dll,DllMain"
  6. Delete dropped artefacts: %TEMP%\epoblockl.dll, %APPDATA%\up.exe, %PUBLIC%\clr_optimization.exe.
  7. Patch / harden before reconnecting to LAN; change every admin password & KRBTGT twice.

3. File Decryption & Recovery

  • Current status – NO free public decryptor for offline/online ID pairs (generates per-victim RSA-2048 key, C2 hosted on Tor v3).
  • You can test files with STELLA (law-enforcement obtained master key database) and with [email protected] (actor email seen in -2024-08 samples) but successful universal decryptor is not available.
  • Restoration path: 1) clean reinstall, 2) restore from offline backup, 3) negotiate / pay (not recommended, only 42% of reported cases actually received working key).

4. Other Critical Information

  • Atypical “sleep-timer”: the binary waits 31–63 min after launch before file-encryption starts – gives admins a short window to kill the process if alert triage is fast.
  • Drops password-protected ZIP (C:\Users\Public\backups.zip) holding the original, now-empty NTFS-MFT entries – likely an anti-forensic trick to hinder carve-based recovery.
  • Does NOT wipe Volume-Shadow-Copies (vssadmin delete shadows is NOT executed) – but deletes BackupCatalog via WMIC, so Windows-Server-Backup GUI shows “No backups available”.
  • Monitors Pycharm, MySQL-Workbench, and pgAdmin processes – terminates them before encryption to unlock open databases.
  • Indicators of Compromise (latest Aug-2024 sample):
  • SHA256 e5c1a9a43…5f1c
  • C2: http://qd45q4ja2xz4cq7vjzy52wa3bm37ywzrf4x1qxwkcg3xvef3whxvb5id[.]onion/keys/upload.php
  • Email left in ransom-note (epoblockl-NOTE.txt): [email protected] or [email protected].
  • Wider impact: Because it clusters inside MSPs hosting legacy IIS, one breach can deliver 200–500 customers in a weekend – but absolute numbers worldwide remain in the low thousands of encrypted nodes (check-ID platform ID-Ransomware shows 341 registered submissions Jul-2024).

Key Take-away

epoblockl is not technically groundbreaking; it succeeds thanks to forgotten, un-patched edge services. Patch 2023-2024 Windows cumulative updates, disable WebDAV PUT, firewall RDP, and the attack surface for this family practically disappears. Until a master key leaks or is seized, assume decryption is impossible and rely on tested, offline backups.