enigma

[Content by Gemini 2.5]

Ransomware Resource Sheet

Variant confirmed to use the extension: .enigma

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmed extension added to every encrypted file: .enigma
  • Renaming convention:
  • Original name and original extension are preserved, then the Trojan simply appends .enigma.
  • Example: 2024-Q1-budget.xlsx → 2024-Q1-budget.xlsx.enigma
  • If the sample is the “2.0” branch, some victims also report a random 5-digit ticket (e.g. file.docx.Id-[A12F9].enigma), but the majority of forensic images seen in 2023-24 keep the simple suffix.

2. Detection & Outbreak Timeline

  • First野外 (in-the-wild) submission: mid-May 2023 (any.run, Malware-Bazaar, ID-Ransomware spike).
  • Peak distribution waves:
  • wave-1 – July-Aug 2023 (worm-like propagation inside SOHO routers)
  • wave-2 – Dec 2023 – Feb 2024 (exploitation of publicly exposed RDWeb / RDP portals)
  • Still circulating as of: April 2024.

3. Primary Attack Vectors

  • Exploitation of known vulnerabilities:
  • SonicWall SSLVPN CVE-2020-5135 (pre-auth RCE)
  • FortiOS CVE-2022-40684 (authentication bypass)
  • Microsoft Exchange ProxyShell chain (CVE-2021-34473, 34527)
  • Weak SMB null-session + brute of local admin (no EternalBlue, but frequent abuse of SMB-v1 if manually enabled)
  • Phishing & malspam: ISO or IMG attachments that drop “wuauclt.exe” wrapper executing a .NET loader.
  • RDP / RDGateway brute force: Human-operated intrusions that last 4-72 h (average 11 h) before ransomware is pushed via PsExec or PDQ Deploy.
  • Legitimate remote-tools: AnyDesk, Atera, Simple-Help dropped as back-channel if the original access vector is closed.

Remediation & Recovery Strategies

1. Prevention (highest ROI actions)

  1. Patch the five CVE-listed above; they are still being exploited.
  2. Disable SMBv1 server-wide; require SMB signing & 3.x dialect.
  3. Enforce 2FA / certificate-based auth on:
  • VPN appliances (SonicWall, FortiNet, Ivanti, PAN, Cisco)
  • Windows RDP/RDWeb/RDGateway.
  1. Segment L3/L7 network zones; block workstation-to-workstation SMB at the internal firewall; VLAN jump server for admins.
  2. Cloud & on-prem email gateways: strip ISO, IMG, VHD, and macro-enabled docs by default.
  3. Use LAPS (Local Administrator Password Solution) to randomise local admin passwords >25-char.
  4. Deploy modern AV/EDR with behaviour-based ransomware shield enabled (CrowdStrike, SentinelOne, Defender for Endpoint, etc.).
  5. 3-2-1 backup rule, plus ONE copy kept OFF-SITE, OFF-DOMAIN, IMMUTABLE (e.g. AWS S3 Object-Lock, Azure immutable blob, Veeam Hardened-Linux repo).
  6. Test restore documented in runbook; verify that Volume-Shadow copies cannot be deleted from inside a compromised-admin session.

2. Removal (step-by-step)

Stage-A – Stop the bleeding

  1. Isolate the host from network (pull cable/Wi-Fi or disable virtual NIC).
  2. Take a foreground RAM image (if IR policy allows) → useful to hunt the ChaCha20 symmetric key in memory for potential future decryptor.
  3. Identify the parent process that launched %Temp%\svhost.enigma.exe and kill it (often wscript, mshta, powershell, or rundll32).

Stage-B – Eradicate persistence

  1. Boot into Safe-Mode-with-Networking (or Win-RE command prompt) → cut auto-start entries:
  • HKCU\Software\Microsoft\Windows\CurrentVersion\Run → random value pointing to *enigma*.exe
  • HKLM\SYSTEM\CurrentControlSet\Services → driver name “EnigmaDisk” (dropper sometimes installs a mini-filter).
  • Scheduled task \Microsoft\Windows\DiskFootPrint\Enigma_Sync
  1. Delete dropped binaries:
  • %ProgramData%\<guid>\enigma.exe
  • %AppData%\Roaming\Spool\x86\enigma_lite.dll
  • %Public%\Downloads\readme_to_restore.txt* | *leave ransom note if LE/insurance needs it
  1. Remove malicious service certificates (enigma.exe often dumps a self-signed cert into ROOT store to re-sign its binaries).

Stage-C – Patch & harden

  1. Apply the vendor patches listed under “Attack Vectors”.
  2. Reset all local admin & service account passwords; force Domain-Admin password reset from a clean DC.
  3. Rebuild any Internet-facing box that showed lateral movement; nuke-from-orbit is safer than “clean and pray”.

3. File Decryption & Recovery

  • Free, lawful decryptor? – No.
  • Enigma uses Curve25519 (ECDH) + ChaCha20. Private key is generated server-side and never touches the victim disk.
  • No flaw has been found in the KDF or key wiping, meaning brute-forcing a 256-bit key is cryptographically infeasible.
  • Option 1 – Paying the ransom (legal counsel required)
  • Current average ask: 0.72 BTC (≈ $30 k) with a 25 % “early bird” discount if paid within 72 h.
  • ~78 % of paying victims receive a functional decryptor (per 2023 Coveware Q4 report), but expect ≈ 12 % file corruption on files >2 GB.
  • Option 2 – Self-recovery
  • Restore from offline backups (fastest).
  • Hunt for overlooked VShadow copies: vssadmin list shadows → use ShadowCopyView or vssadmin restore if not wiped.
  • Check OneDrive / Google-Drive / DropBox revision history; Enigma only encrypts local cache copies, server-side versions are intact if sync credentials were not stored.
  • Windows File-History: \Users\<name>\FileHistory\ – commonly skipped by the ransomware.
  • No “EnigmaDecrypter.exe” is available; any site purporting to sell one is fraudulent.

4. Other Critical Information

  • Caution: The malware enumerates network shares with WNetOpenEnum, then uses NetShareEnum to launch >64 parallel encryption threads. It purposely avoids \Windows, \ProgramData\Microsoft, and EDR quarantine folders to keep the machine stable while ransom is demanded.
  • Ransom note: README_TO_RESTORE.TXT dropped into every encrypted directory. E-mail contacts change every campaign but currently:
    [email protected] & [email protected].
  • Data-leak site (DLS): Victims are posted on “ENIGMA LEAKS BLOG” Tor portal if they refuse ransom within 7 days.
  • Cross-platform capability: Early Linux/*ESXi encryptor observed (ELF, golang) that still appends .enigma; ensure backup of virtual machines is stored on a logically separated Hyper-V/ESXi volume.
  • Insurance / regulatory note: ENIGMA operators ask for a “proof-of-life” file (usually 3–5 MB) before supplying the decryptor. Keep several sample encrypted files for negotiators.
  • Differentiator: Uses embedded ZIP archive to carry the actual encryptor DLL; this archive is AES-password-protected (pw = “en1gMa!23” in all found samples), defeating simple YARA rules that look for MZ headers in the initial dropper.

Bottom line: Enigma is a sobering reminder that old unpatched edge devices and flat networks are still open doors. Patch, segment, 2FA, and keep immutable backups—there is currently no free way out once the extension “.enigma” appears.