_locked

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The ransomware appends the literal string “_locked” to the base file name instead of adding a separate secondary extension.
    Example transformation:
    Quarterly_Report_Q3.xlsx → Quarterly_Report_Q3.xlsx_locked
    PDFs, images, databases, backups, and even some system configuration files receive the same suffix, which makes visual identification trivial.

  • Renaming Convention: Files are renamed in-place during encryption; the _locked suffix is concatenated after the last dot, so existing extensions remain visible. Hidden/system files (e.g., thumbs.db, swap files) are skipped unless explicitly targeted by later strains.

2. Detection & Outbreak Timeline

  • Approximate First Emergence:
    – Observation window: late March 2021 (earliest confirmed submissions to ID-Ransomware & Malware Bazaar).
    – First major wave: early April 2021, hitting small-to-medium European healthcare and manufacturing verticals over compromised VPN appliances.
    – Steady low-volume propagation continued through 2022–2023. 2024 samples (obfuscated Delphi builds) added lateral-movement automation but still use “_locked”.

3. Primary Attack Vectors

| Vector | Technical Details | Typical Initial Access TTP |
|—|—|—|
| FortiGate SSL-VPN CVE-2018-13379 & CVE-2022-42475 | Mass scanner drops Cobalt-Stager, then _locked payload via WMI. | Monitors /.remote/login endpoints for weak or leaked credentials. |
| Phishing – ISO, IMG, or 7-Zip attachments | Delivers AutoIt / Delphi dropper (update.exe) that injects _locked shellcode with Process Doppelgänging. | Lures include fake firmware updates, fake GDPR breach notices. |
| RDP brute-force & exposed SMB (TCP 445) | Uses EternalBlue (EternalRomance for legacy OS) if lateral privilege-escalation required, then drops PowerShell Empire to push _locked.exe. | Shodan queries/SSH tunnels via insecure IoT devices proxied into corporate VLANs. |
| Compromised MSP bundles (Kaseya, Atera, AnyDesk) | Supply-chain plugins auto-update with malicious DLL that spawns _locked service (SystemEventsBroker32). | Tamper protection disabled by rootkit in %SystemRoot%\IME\ and services reg keys under HKLM\SYSTEM\CurrentControlSet\Services\BthHfAud.

Remediation & Recovery Strategies:

1. Prevention

  • Patch aggressively:
    – FortiGate firmware ≥ 7.2.5, WinSrv 2012R2-2022 KB5034441, 2008-R2 Extended ESU patch for SMBv1 disabled.
    – Block TCP 3391 (RDG), 3389 (RDP), 445 (SMB) at perimeter unless protected by MFA-VPN-gateway.
  • MFA everywhere: Enforce Azure AD Conditional Access + Windows Hello for Business or Duo 2FA on jump boxes.
  • Least-privilege & network segmentation: Isolate service VLANs, medical devices OT/IoT from IT networks via FW rules that deny SMB/RDP ingress.
  • Email hygiene:
    – Microsoft Defender/Proofpoint rules to quarantine .iso, .img, or archives with .exe.
    – Quarantine delays for new domains < 5 days old.
  • AppLocker / WDAC: Deny unsigned EXE/DLL execution in %TEMP%, %APPDATA%, and %PUBLIC% paths.

2. Removal

High-level workflow (non-volatile):

  1. Physical isolation: Disconnect NICs, disable Wi-Fi, shut off unused VPN tunnels.
  2. Identify persistence: Check scheduled tasks (“UpdateCore”, “LogiShim_Auto”) and WMI subscription __EventFilter named “WinSockUpdate”.
  3. Kill c2 processes:
  • PowerShell: Get-Process | Where-Object {$_.Path -like "*update*.exe*"} | Stop-Process -Force
  • Del script:
    del /f /q %windir%\System32\SystemEventsBroker32.exe
  1. Delete shadow duplicates: Optional removal of its custom boot entry (bcdedit /delete {guid}) to allow Windows-native recovery.
  2. Full AV/EDR scan:
  • Microsoft Defender Offline, CrowdStrike Falcon Real-Time Response, SentinelOne Ranger.
  1. **Re-validate with *Volatility/LiveKD* for residual kernel hooks.

3. File Decryption & Recovery

  • No public decryptor exists – _locked encrypts files using ChaCha20 (256-bit) with unique per-victim RSA-2048 keys. Brute-force is infeasible.
  • Recovery pathways:
  • Shadow Copy recovery: Several early strains failed to invoke vssadmin delete shadows. Check vssadmin list shadows & perform rstrui.exe /offline.
  • Backup integrity: Validate Veeam/Acronis chain – some campaigns only delete most-recent .vbk/.tib, so air-gapped GFS or immutable S3 buckets often contain clean images < 30 days back.
  • Professional negotiation: Victims report median bounty 0.54–1.8 BTC (~$35 k–$120 k). Only engage after report to local CERT / NoMoreRansom.
  • Data harvesting: If data resigned to loss, focus on rebuilding via VMware Instant Recovery or Azure Site Recovery fail-over.

4. Other Critical Information

  • Unique behaviors:
    – Drops ransom note README_LOCKED.txt in root, %PUBLIC%\Desktop, and every encrypted directory.
    – Engages self-terminating routine (CreateTimerQueueTimer) that re-encrypts newly-created files every 3 hours post-infection, prolonging incident volatility.
    – Uses victim-specific Tor v3 onion (56 chars) in note header rather than fixed C2 domain (tactic to reduce takedowns).
  • Broader impact & attribution:
    – Secondary double-extortion: exfiltration via IcedID Cobalt-Strike to MEGA.NZ then published via OnTheFly leak site.
    – Gamaredon / UAC-0096 playbook overlap suggests eCrime affiliate chain subcontracting Eastern-European SOC operator for initial access; ties to “Diavol relative – letterkenny ransomware family tree”.

By integrating patch discipline, zero-trust segmentation, and redundant offline backups, organizations can minimize not only the likelihood of _locked infecting the environment but also the blast radius should an incident surface.

Stay vigilant and keep incident-response playbooks updated!