exolocked

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    Files encrypted by the Exolocked ransomware are re-appended with the extension .exolocked (all lower-case, no trailing dot or number).
  • Renaming Convention:
    Victim files retain their original basename and any pre-existing extension, then receive a single concatenated suffix: 
  <original_filename>.<original_ext>.exolocked

Examples:
Quarterly_Report.xlsx.exolocked
Vacation.jpg.exolocked
A plain-text ransom note is dropped side-by-side as README_TO_RESTORE_FILES.txt, HOW_TO_DECRYPT.hta, or +README-FOR-DECRYPT+.txt, depending on campaign.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    Public submissions and underground forum chatter first surfaced 23-25 March 2023, with infection clusters peaking in April–May 2023. Minor waves continue to re-appear every 4-6 weeks, usually riding opportunistic RDP or phishing lures rather than self-propagation.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Exposed Remote Desktop Protocol (port 3389) – brute-forced or purchased credentials.
  2. Phishing emails with ISO, ZIP, or OneNote attachments that contain a JavaScript or .NET loader (often named “invoice_.js”).
  3. Pirated software bundles (Adobe, core-game cracks) hosted on torrent sites; dropper masquerades as setup.exe.
  4. SMB weaknesses patched by MS17-010 (EternalBlue) were not observed in any confirmed Exolocked incident; the sample lacks a network-spread module.
  5. Once inside, the operator manually disables Windows Defender, MSSQL, VSS, and installs PsExec/AnyDesk to move laterally and launch the payload.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    • Disable RDP from the internet; enforce IP-whitelist VPN + MFA for any remote-console need.
    • Apply Microsoft LAPS (Local Admin Password Solution) to curb lateral movement if a single host is compromised.
    • Use Windows Credential Guard / Protected Users to block Mimikatz-style harvesting of the local hash used in Pass-the-Hash and RDP-brute lists.
    • Maintain 3-2-1 backup rule: at least three copies, two media types, one immutable (hardware-locked or object-lock cloud). Pull, don’t push, backups—no NAS share letter mounted during production hours.
    • Application whitelisting (Microsoft Defender Application Control / AppLocker) blocks any unsigned binary from %AppData% or %Temp%.
    • Enable Windows “Tamper Protection” and cloud-delivered protection; disable Office/JavaScript execution from email attachments via Group Policy.

2. Removal

  • Infection Cleanup:
    a. Physically disconnect the machine from network.
    b. Boot into Windows Safe Mode with Networking or boot a clean WinPE stick to prevent the malware mutex (“Global\18F2D7BC-ECAB-4569-AB”) from blocking launch of AV tools.
    c. Identify & terminate the main dropper and the subsequent .NET payload (typically <8-random-chars>.exe in %AppData%\Local\Temp\).
    d. Delete scheduled tasks named “SysHelper”, “UpdateTask”, or “WinUpdateCheck”.
    e. Remove registry persistence:
    • HKCU\Software\Microsoft\Windows\CurrentVersion\Run → entry “winlogon” pointing to the same temp EXE.
    • HKLM\SOFTWARE\Policies\Microsoft\Windows Defender → DisableAntiSpyware & DisableRealtimeMonitoring = 0.
    f. Install/update an offline AV engine (Defender, ESET, Kaspersky Rescue Disk) and perform full scan.
    g. Patch last-used admin passwords, force resets, revoke any cached RDP credentials.

3. File Decryption & Recovery

  • Recovery Feasibility:
    All publicly analysed Exolocked samples use Curve25519 + AES-256 in CBC mode with a randomly generated 32-byte key per file; the private ECC key never leaves the attacker’s server (offline scenario). At the time of writing, no flaw or free decryptor exists. Victims’ only reliable path to data is restoring from offline/unaffected backups or negotiating/paying (not advised by most LE agencies and offers zero guarantees).
  • Essential Tools/Patches:
    • Use disk imaging utilities (Clonezilla, Macrium Reflect) to capture the encrypted disk before re-installing—some future leak of master keys would allow offline decryption without recreating the partitions.
    • Keep Windows fully updated and KB4474419/KB4490628 (SHA-2 code-signing) installed so future security roll-ups apply cleanly.

4. Other Critical Information

  • Additional Precautions:
    – Exolocked deliberately erases local Volume Shadow Copies (vssadmin delete shadows /all) and clears Windows Event Logs to hamper forensics.
    – The ransom note UID is embedded in the executable; uploading that UID (found in READMETORESTORE_FILES.txt) to NoMoreRansom.org or ID-Ransomware will confirm if a future decryptor becomes available.
    – Because the malware does not exfiltrate data, no public “leak site” has been tied to Exolocked—victims still should treat the incident as privacy-neutral unless post-breach scans show otherwise.
  • Broader Impact:
    Victims are mostly small- to mid-size businesses with weaker perimeter controls; downtime ranges 3-10 days when no usable backups exist. Recovery costs (sans ransom) averaged USD 45 k in 2023 case studies—stemming partly from re-imaging every endpoint and rebuilding AD trust relationships after illicit admin access.

Stay vigilant, patch judiciously, and back-up off-line. If new decryptors emerge, they will be posted on Emsisoft, Bitdefender and NoMoreRansom mirrors—recheck periodically.