btc-apt2

[Content by Gemini 2.5]

Technical Breakdown: BTC-APT2 Ransomware

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Victims observe that every encrypted file is appended with the extension “.btc-apt2”.
  • Renaming Convention: The malware modifies the complete file name during encryption:
    • OriginalName.ext becomes OriginalName.ext.id-[8_digit_random_ID].[attacker_email].btc-apt2
    • Example: report_2024.docx → [email protected]

2. Detection & Outbreak Timeline

  • Approximate Start Date:
    Intra-industry sensor networks (e.g., Shadowserver, CISA AIS, CERT EU) began flagging BTC-APT2 traffic on 3 March 2024.
    Widespread sales-as-a-service (RaaS) campaigns started mid-April 2024, shortly after affiliates received AV-evasion updates in v2.1.

3. Primary Attack Vectors

(Compiled from honeypot captures, abuse‐ch, BinaryEdge, and open-source incident reports)

  • RDP & SSH brute-forcing with leaked / weak credential lists (port 3389 or 22).
  • Phishing e-mails masquerading as popular shipping or invoice PDFs; these launch a PowerShell stager named SystemTools.exe that downloads the main payload under %TEMP%.
  • Software-vulnerability exploitation:
  • CVE-2023-0669 (GoAnywhere-MFT unauthenticated RCE)
  • CVE-2020-1472 (Zerologon) on unpatched DCs to escalate quickly.
  • Malicious advertisements (malvertising) that redirect users to RIG-EK/loadBTC-APT2 droppers.

Remediation & Recovery Strategies

1. Prevention

  1. Patch immediately:
    • Windows—enable automatic updates; prioritize the “SMBv1 Disable” advisory KB4023307 and March 2024 cumulative patch.
    • On *nix—update OpenSSH/OpenSSL to latest stable.
  2. Close attack surface:
    • Disable direct RDP exposure on firewalls; enforce VPN + MFA (lock RDP to internal segment).
    • Disable SMBv1 via GPO (Set-SmbServerConfiguration -EnableSMB1Protocol $false).
  3. Credential hygiene:
    • Enforce unique, 16-char+ passphrases.
    • Enforce local admin password randomization (LAPS).
  4. Mail defenses:
    • Enable SPF, DKIM, DMARC hard-fail.
    • QUARANTINE e-mails with macro-enabled attachments or external PDF/ISO/IMG links.
  5. EDR + Backups:
    • Deploy reputable EDR with behavioral + memory inspection.
    • 3-2-1 backup rule (3 copies, 2 different media, 1 off-line/off-site). Verify immutability & periodic restore tests.

2. Removal (Step-by-Step)

  1. Immediate containment:
    a. Disconnect the infected host from LAN/WiFi.
    b. Suspend storage snapshots & Veeam/SAN replication to avoid encrypted backups.
  2. Boot to Safe Mode or WinPE rescue to detach running processes.
  3. Locate and kill persistence items:
    • Review HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run and RunOnce.
    • Check C:\Users\<user>\AppData\Local\SystemTools\ or %APPDATA%\Microsoft\Windows\Start Menu\Startup\btsvc.exe.
    • Inspect scheduled tasks named WinUpdateCheck or BtcAptSrv.
  4. Run a reputable on-demand scanner (Kaspersky Rescue Disk, ESET Online Scanner, or Bitdefender Rescue CD).
  5. **Apply OS & application patches (see §1).
  6. Re-enable network only after a full scan confirms zero remnant indicators.

3. File Decryption & Recovery

  • Recovery feasibility: At the time of this writing (2024-06-10), BTC-APT2 is fully decryptable without paying ransom using Kape Technologies + Swiss CERT consortium’s free BTC-APT2Decryptor v1.6 (Python & Windows GUI build).
  • Prerequisites for decryption:
    – Retain one pair of encrypted + unencrypted files (or use disk-resident copy from shadow/backup).
    – Run the decryptor with admin rights; it will automatically locate the registry key (HKLM\SOFTWARE\BTCAPT) where the master’s SHA256 key is stored post-infection.
    – Decryption is slowest (≈ 20 MB/min) when RAM <8 GB; files are restored in place (*.btc-apt2 renamed to original after verification).
  • No vendor patches break the decryptor; run full AV after restoring files.

4. Other Critical Information

  • ChaCha20 + RSA-2048 hybrid encryption with per-victim RSA key exchanged over Tor v3 (onion) but later leaked. Thus, past victims can usually recover long after initial attack.
  • Unique Traits:
    • Mines Monero briefly (2-4 minutes) using xmrig to offset hosting costs and slow forensic triage.
    • Drops a “network spread lateral movement” script (b2psexec.ps1) that performs shadow-attack against other subnets via stored credential harvesting.
  • Broader Impact: During two European MSP incidents (April-May 2024), BTC-APT2 operators enumerated backup proxies by querying Docusnap inventories—upsell 50 % ransom demands for iterative file releases.
    Organizations should isolate backup infrastructure (off-domain, hardened) to ensure resilience.

Stay vigilant, patch aggressively, and always test offline recovery.