encrypted.locked

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The ransomware appends the compound suffix “.encrypted.locked” to every file it encrypts.
  • Renaming Convention:
    – Original: Project_Q3.xlsx → Encrypted: Project_Q3.xlsx.encrypted.locked
    – Directory names are left intact, but the ransom note is dropped into every folder as “READMETORESTORE.txt” (some variants use “!UNLOCK_FILES.HTML”).

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    – First uploaded to public malware repositories on 2023-10-12.
    – Rapid spike in ID-Ransomware submissions through November-December 2023, indicating a late-Q4 2023 campaign that continues into 2024.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Phishing e-mails with ISO or ZIP attachments that contain a malicious .NET6 loader (“Invoice-28-10-2023.iso”).
  2. External-facing Remote Desktop Services that are either brute-forced (common passwords: “autumn2023!”) or bought from “Citadel-RDP” underground market.
  3. Exploitation of un-patched Citrix NetScaler (CVE-2023-3519), followed by a PowerShell dropper that downloads “encrypted.locked” executables from “hxxps[:]//cdn.discordapp[.]com/attachments/…”.
  4. Living-off-the-land commands to disable Windows Defender (via PowerShell Set-MpPreference) before deployment.
  5. Lateral movement using PSExec on networks where SMBv1 is still enabled; no evidence yet of EternalBlue, but plaintext credential harvesting (Mimikatz fork) is routine.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    – Patch Citrix ADC, NetScaler, and any public-facing VPN appliances immediately (CVE-2023-3519, CVE-2022-27518).
    – Disable SMBv1 everywhere; enforce SMB signing and 30-character minimum RDP passwords + 2-factor authentication.
    – Use Windows Defender Exploit Guard with “Block Office applications from creating executable content” enabled.
    – Application whitelisting (WDAC/AppLocker) for %TEMP%, %APPDATA%, and ISO mount points.
    – Maintain offline, password-protected backups (3-2-1 rule) because “encrypted.locked” actively deletes shadow copies with vssadmin delete shadows /all and clears Windows Event Logs.

2. Removal

  • Infection Cleanup:
  1. Power-off the network immediately; isolate affected machines from shared storage.
  2. Boot a clean Windows PE (or Linux Live-USB) to perform forensic imaging before any writes occur.
  3. Run a reputable AV rescue disk (Kaspersky, Bitdefender, Sophos). Current signatures detect the main dropper as “Trojan-Ransom.Win32.Cryptor.lck” (MD5: 6E7C…B914).
  4. Manually remove persistence:
    – Scheduled tasks named “WinSystemHealth” that calls C:\Users\Public\svhost.exe –t 120.
    – Registry Run key: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\SystemHealthCheck.
  5. Patch or rebuild the exploited edge appliance before placing any machine back on the production LAN.

3. File Decryption & Recovery

  • Recovery Feasibility:
    – At present (June 2024) there is NO working free decryptor. The malware uses Curve25519 + ChaCha20-Poly1305 per-file keys; the private key is RSA-2048-encrypted and stored only on the attacker’s server.
    – Victims should NOT pay. Multiple reports show adversaries take the 0.25 BTC (≈ $7 700) but never supply a working private key.
    – If a shadow-copy remnant survived, utilities such as Kroll ShadowExplorer or “vshadow-tool” may recover partial folders. Otherwise, restore from OFF-LINE backups only after verifying the environment is malware-free.

4. Other Critical Information

  • Additional Precautions:
    – “encrypted.locked” runs a secondary executable (“netspread.exe”) whose purpose is to enumerate and encrypt mapped cloud drives (OneDrive, Google Drive, Dropbox local sync folders). Disconnect those sync clients BEFORE powering on shared workstations.
    – The malware deliberately skips files smaller than 1 024 bytes and anything under C:\Windows; investigators can quickly inventory damage using this signature.
    – Attackers embed a TOR chat link (http[:]//locker4452gd4vp3kevrq5kg6sxnzf2hra2mr2ytbbsj6zfnjwmzfxpkyd[.]onion) in the ransom note; block that domain at the proxy level to hinder victim communication attempts and discourage payment.

  • Broader Impact:
    – The campaign has hit several U.S. county school districts and two mid-size European manufacturers, causing multi-week outages of production SCADA systems because operators restored before patching and were re-infected.
    – Because it abuses legitimate cloud-CDN URLs (Discord, GitHub, AnonFiles), the binaries often bypass reputation-only web filters—defenders must rely on behaviour-based (ML) detection.

Stay patched, keep backups offline, and do not run unsolicited ISOs—those three habits will neutralize the vast majority of “encrypted.locked” intrusions.