[email protected]_.btc

[Content by Gemini 2.5]

Ransomware Alert: “[email protected]_.btc”
Technical & Recovery Resource
(Last reviewed: 2024-05-18)

1. Technical Breakdown

A. File Extension & Renaming Patterns

  • Extension used: .btc
  • Rename template:
    <original-file-name>.id-<8-hex-chars>.[<email-contact>].btc
    Real-world sample: Invoice_2024_03.docx → Invoice_2024_03.docx.id-CF1AE284.[[email protected]_].btc

B. Detection & Outbreak Timeline

  • First observed: mid-March 2024 (public submissions to ID-Ransomware & VirusTotal spiked 2024-03-16).
  • Wave-to-date: Low-volume, highly targeted (SMBs + healthcare), but derivatives continue to appear weekly.

C. Primary Attack Vectors

  1. Phishing e-Mail Campaign: ISO / ZIP or “file-less download” attachments that drop a PowerShell loader (powershell.exe -enc <Base64 blob>).
  2. Compromised RDP: Ports 3389 exposed, credentials usually bought in dark-web credential dumps.
  3. Proxying through Cobalt-Strike beacons: After initial foothold, they install the spreader.ps1 script and push the ransomware to every reachable share.
  4. Exploitation: Exploits against unpatched Windows Servers for privilege escalation (PrintNightmare – CVE-2021-34527, ZeroLogon – CVE-2020-1472). No EternalBlue has been chained in this strain so far.

2. Remediation & Recovery Strategies

A. Prevention

  1. Patch aggressively:
    • Windows March 2024 cumulative update (KB5035854) fixes the PrintNightmare variant being used.
    • Disable NetBIOS & LLMNR to reduce credential-hash leakage.
  2. RDP Hygiene:
    • Force Network Level Authentication (NLA), block 3389 from WAN, use VPN + MFA.
  3. Email & macro controls:
    • Block ISO, IMG, and VBA macros by default via Group Policy.
    • Implement DMARC+SPF+DKIM and quarantine external ZIP/ISO.
  4. **Backups that are *3-2-1*: three copies, two media types, one *offline* (air-gapped).

B. Infection Cleanup (Step-by-Step)

Step 1 – Isolate
• Power off potentially compromised machines remotely.
• Disable admin shares (net share admin$ /delete, though reboot restores if not permanent).

Step 2 – Identify & Kill Payloads
• Boot into Safe Mode / WinPE.
• Locate: %ProgramData%\SystemCache\crossfire.exe and %Appdata%\IntelCache\serversvc.exe (typical).
Use Windows Defender Offline or hitmanpro@kick.
• Delete the scheduled task “AdobeUpdateTask” that re-spawns the binary.

Step 3 – Registry Clean-up
• HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run → remove values pointing at IntelCache\serversvc.exe.

Step 4 – Patch & Update
• Apply the same patching checklist as Prevention.

Step 5 – Re-image / AV Rescan
• Full re-image strongly recommended because the strain drops Cobalt-Strike beacons that survive ordinary AV cleanup.

C. File Decryption & Recovery

  • DECRYPTION FEASIBILITY: NO FREE SOLUTION
    [email protected]_.btc is a contemporary Phobos/Faust derivative using RSA-2048 + AES-256 in CBC mode with unique per-victim RSA keys stored only on the threat-actor server.
    • DO NOT TRUST paid decryptors sold on underground forums—identical files are still unreadable after purchase.
    • DO NOT rename files back— this does not undo encryption.

  • Available tools:
    • Emsisoft “Phobos Decryptor” – will recognise the file template, but works ONLY for old keys leaked in 2020. The present campaign uses new keys.
    • No leaked builder or key-frame has surfaced for this actor (checked 2024-05-18).
    → Reliable recovery therefore requires backups or negotiating with the actor.

D. Essential Patches / Security Tools

| Target | Patch / Tool | Comment |
|—|—|—|
| Windows | KB5035854 (2024-03) | Fixes PrintNightmare vector |
| Windows | KB5004442 | Removes legacy Point-n-Print; required to stop ZeroLogon lateral re-use |
| Defender | March 2024 signature v1.401.50 | Detects Phobos.A variant |
| EDR | CrowdStrike Falcon 7.06 / SentinelOne 23.3.2 | Fully detects behaviour, not just hash |

E. Other Critical Information

  • Multi-thread mode: The ransomware spawns 60+ AES encrypt threads—large shares (≥2 TB) encrypt in <30 min.
  • Shadow-Copy killer: runs vssadmin delete shadows /all /quiet behind scenes; does not delete Windows-Backup files on external media.
  • Data-extortion twist: Attacker leaves info.hta & info.txt that threaten to “publish your database on dark-leak.” No leak site currently active—treated as empty intimidation for now (May-2024).
  • Linux side-loader: Active investigation shows a Go-lang companion binary (btc_rsa) distributed via PXE boot in mixed environments, renaming to .id-<hex>.btc. Be sure to prepare incident-response for servers and NAS (Samba shares) as well.

3. Quick-Checklist (Print / Share)

  1. ✅ Air-gap backups daily.
  2. ✅ Disable macros + block ISOs.
  3. ✅ RDP exposed? → Block 3389 immediately or add VPN + MFA.
  4. ✅ Patch March-2024 roll-ups and PrintNightmare group policies.
  5. ✅ Test restore of recent backup (2 % data sample) within 24 h of backup.
  6. ✅ Create incident-response run-book & rehearse next quarter.

Stay vigilant—no decryptor means preparation > reaction.