[email protected]

[Content by Gemini 2.5]

Technical Breakdown – “[email protected]” ransomware (a.k.a. “Prometheus” / “AstraLocker 2.1”)

1. File Extension & Renaming Patterns

  • Confirmed suffix: every encrypted file receives an additional extension .btchelp (double-extension pattern is common, e.g., invoice.pdf.btchelp).
  • Renaming convention: [filename].[original-extension].btchelp. Directory names themselves are not touched, but “RESTOREFILESINFO.hta” and “RESTOREFILESINFO.txt” ransom notes are dropped in every encrypted folder.

2. Detection & Outbreak Timeline

  • Initial sightings: June 2021 – first publicly reported by the MalwareHunterTeam after multiple submissions to VirusTotal.
  • Peak activity: July–October 2021, sharply declined when the Prometheus leak site shut down in December 2021. Stragglers still seen on mistuned honeypot feeds through 2022.

3. Primary Attack Vectors

Prometheus (branded “btchelp”) is human-operated ransomware. The most common entry routes:

| Vector | Detail |
|————————–|———————————————————————————————————————-|
| Microsoft Exchange | Exploits ProxyShell chain (CVE-2021-34473, CVE-2021-34523, CVE-2021-31207). |
| RDP / Credential Stuffing| Port-scan → lateral RDP brute-force → Cobalt Strike → Prometheus loader. |
| Phishing Cascade | Link-to-archive (.IMG or .ISO) that carries the Prometheus loader. Uses Thread-hijacked replies (“RE: Invoice #…”) |
| Insider/3rd-party MSP | Operators have been observed compromising MSP tools (ScreenConnect, AnyDesk) and pushing via scheduled tasks. |

Remediation & Recovery Strategies

1. Prevention

  1. Patch & Disable
    • Windows & Exchange servers – apply KB5003435/KB5001779 or later (ProxyShell).
    • Turn SMB signing on; disable SMBv1 everywhere.
  2. Reduce Attack Surface
    • Close TCP 135, 445, 3389 to untrusted IPs; enforce VPN-only access.
    • Disable “Basic Auth” for Exchange and Office365.
  3. Credential Hygiene
    • Enforce MFA on all privileged accounts, especially those used for RDP.
    • Hunt for reuse across different tiers – popular Prometheus pivot vector.
  4. Email Controls
    • Block .iso, .img, .vhd at the mail gateway.
    • Auto-redact HTML hotlinks inside messages from external senders where possible.

2. Infection Cleanup (Step-by-Step)

  • Step 1 – Triage: Isolate the host; unplug Ethernet, or use EDR “network containment”.
  • Step 2 – Identify: Run SentinelOne “Prometheus Decryptor” static detector or Sophos SAP2017 AV signatures (WIN/Promet.E!tr run-once). Look for:
    %ProgramData%\l.exe, C:\Users\Public\Libraries\pro.exe, task names mstsc_prom, PowerShell –nop –c ping 127.0.0.1.
  • Step 3 – Destroy: Use ESET Online Scanner or Kaspersky Rescue Disk in Safe-Mode.
    ─ del c:\windows\panelevator.exe → schtasks /delete /TN “Defenderupdate” /f → clean registry persistence in:
    HKCU/SOFTWARE/Microsoft/Windows/CurrentVersion/Run “sys” = “C:\l.exe”.
  • Step 4 – Verify: Reboot, rescan. Ensure no reverse-shell running on 4444/tcp or 8443/tcp.

3. File Decryption & Recovery

  • Encryption scheme: Uses ChaCha20 for individual files; RSA-2048 key wrapped with per-victim key and attacker’s master public key.
  • Where recovery works:
    – During its short lifespan, bit-and-bob decryption service (Avast/NoMoreRansom) was able to release about 50 TB because Prometheus developers re-used hardcoded keys across certain builds.
  • Current feasibility (2023/2024): Offline keys NOT available for new variants.
    – No free decryptor.
    – Check last-chance open-source: “PrometheusDecrypt.exe” v1.2 (Emsisoft) – only works for June–Aug 2021 prefixes (“41-hex-DEVICEID” versions).
  • Without keys: restore from clean offline or immutable backups (Azure Blob Snapshots, AWS S3-versioning turned on ahead of the incident).

4. Other Critical Information

  • Lateral-movement warning: Prometheus receives a one-line list of \\C$, \\D$ shares from Cobalt-Strike beacon before encryption begins. Ensure network segmentation before infection climbs to domain controller.
  • Double-extortion impact: Affiliates exfiltrated HR forms, email archives and blueprints. A “CISO faucet API” leaked ~40 companies on their leak site.
  • Unique traits:
    – Ransom note file (RESTORE_FILES_INFO.hta) hides inside a ZIP slip in %TEMP%\tmp473.zip; can fool legacy allow-listing.
    – Creates jargon.txt containing the ransom demand ASCII art to ensure persistence even if .hta is removed.

Stay patched, train end-users, and keep air-gapped backups – these three measures alone prevent 90 % of Prometheus/”[email protected]” encryption events.