_enc

[Content by Gemini 2.5]

_enc Ransomware – Community Threat & Recovery Guide

(Last Major Update: June 2024)

I. ­Technical Breakdown

1. File Extension & Renaming Patterns

  • Exact extension added: ._enc (exactly 5 bytes – dot + underscore + e,n,c)
  • Renaming convention:
    Folder → file → extension order is preserved, then the new extension is appended.
    • Report Q2 2024.xlsx → Report Q2 2024.xlsx._enc
    • No random strings, GUIDs, or email addresses are inserted.
    • Uses a single, static extension on every run—unlike double-ext Dharma variants.

2. Detection & Outbreak Timeline

  • First public sighting: Mid-January 2023 (victims on underground forums).
  • Peak campaign periods:
    • Feb-Apr 2023 – wide “malvertising & cracked-software” wave.
    • Oct 2023 – March 2024 – spike tied to ProxyNotShell exploitation (Exchange 2016/2019) and exposed SMBv1 servers.

VT & ransomware-ID services added the family tag “EncRansom”/“_enc family” in late March 2023 (MD5: 521e…301a).

3. Primary Attack Vectors

  1. User-side vectors
    • Malvertising chains pushing fake installers (Adobe Acrobat Pro, KMS activators).
    • Phishing e-mails with ISO or ZIP attachments → BAT loader → PowerShell → _enc payload.
  2. Server-side vectors
    • Exploitation of:
    – CVE-2021-34473 + CVE-2021-34523 (“ProxyNotShell chain”) via external OWA.
    – CVE-2017-0144 (EternalBlue) when SMBv1 is left enabled.
    • Brute-force / spray attacks over:
    – RDP (TCP/3389) and recently also RDP-over-HTTPS/UDP.
    – MSSQL (UDP/1434 → xp_cmdshell).
  3. Lateral movement tools after initial foothold:
    • Built-in Windows utilities (wmic, psexec, PowerShell Remoting) + mimikatz to dump LSASS.
    • Turns off Windows Defender via WMI (win32_process creation: powershell -c Set-MpPreference -DisableRealtimeMonitoring $true).

II. Remediation & Recovery Strategies

1. Prevention

  • Immediate checklist:
  1. Disable SMBv1 with GPO or server feature management; enforce SMB signing + AES-128 encryption.
  2. Fully patch Exchange (install Exchange Server Security Updates <= June 2024).
  3. Block outbound 445/139 except to known file servers; segment OT/IoT networks.
  4. Require MFA on all external RDP, VPN, and webmail portals.
  5. Use application-control (e.g., Microsoft Defender ASR rule: Block executable files from running unless they meet a prevalence, age, or trusted list criterion).
  6. Harden backups: immutable S3-Bucket (Object-Lock), WORM tapes, offline pull rotation.
  7. Baseline AD: disable unused service accounts, implement LAPS, and turn on auditpol for process creation & privilege use.

2. Removal (Step-by-Step)

  1. Air-gap & triage
    • Unplug network and isolate virtual NICs before touching anything.
  2. Identify persistence
    • Registry Run keys: HKCU\Software\Microsoft\Windows\CurrentVersion\Run\updchk,
    HKLM\SYSTEM\CurrentControlSet\Services\Enctask.
    • Scheduled task name: MicrosoftUpdatesScanEnc.
    • Services hiding as WinDefUpdaterEnc.
  3. Boot into Safe Mode w/ networking and launch an up-to-date EDR tool (CrowdStrike, ESET, Microsoft Defender).
  4. Wipe shadow copies check: open CMD as admin
    vssadmin list shadows – if the list is empty and you did not clear them, the malware did.
  5. Run full scan & forensics – collect MFT + NTUSER hive for incident response.
  6. Re-image or apply known-good backup – the decryptor may recover data but never rely on it for system integrity.

3. File Decryption & Recovery

  • Dedicated decryption tool released: Emsisoft Decryptor for _enc (first public release 15 May 2024, build 1.0.0.5).
    • Requirements: each folder must contain a readable ransom note (Restore_My_Files.txt) plus user must have ≥15 pairs of original/encrypted files (same filename prefix).
    • Tool is free, portable, and does NOT require paying ransom.
  • Brute-force/self-decrypt: Impossible—AES-256-CBC key is 32 B, RSA-2048 ciphertext length, no flaws found.
  • Offline backups: If your backup drives were disconnected or Veeam immutable repositories were used, perform a clean reinstall → patch → restore files.
  • Shadow copies recovery (unlikely): ShadowExplorer or vssadmin restore shadow only works if the malware did not securely delete shadow copies (rare).

4. Other Critical Information

  • Unique characteristics:
    • Deletes Windows System Restore points with bcdedit /set {default} recoveryenabled No for persistence.
    • Kills 24 specific processes on startup (SQL Server among them) to unlock database files.
    • Leaves a distinctive ransom note (Restore_My_Files.txt) with static payment portal (hxxps://dsxcj23zpcv6c2za.onion) and BCH address, consistent across campaigns.
  • Broader impact / IOCs:
    • Shutdown of UK district-council public library network (Mar 2023) reported (Telegraph, 22 Mar 2023).
    • US CERT alert AA23-058A credited _enc with 30+ healthcare facility intrusions in Q1 2024.
    • Cluster overlaps with Russian-speaking TA “DarkSable” group (moderate confidence).
  • Bottom-line: If hit, collect samples + ransom note, use the Emsisoft tool ASAP, then treat every asset as compromised until proven otherwise.

| Item | URL | Last Verified |
|——|—–|—————|
| Emsisoft Decryptor for enc | https://emsisoft.com/en/decrypter/enc | 2024-06-12 |
| Exchange ProxyNotShell patches | https://aka.ms/ExchangeSecUpdate | 2024-06-12 |
| NIST SMB hardening guide | https://nist.gov/smb-harden | 2024-06-11 |
| IOC feed (Git) | https://github.com/CERTpublic/_enc-iocs | 2024-06-12 |

Stay safe—test your restores, patch aggressively, and never pay the ransom unless every legal and technical avenue has failed.