btc

[Content by Gemini 2.5]

Technical Breakdown: “BTC” Ransomware

1. File Extension & Renaming Patterns

  • Confirmed File Extension: .btc
    The original filename survives, followed by a single dot and the lowercase letters btc. Example:
    2024-Q1_Financials.xlsx → 2024-Q1_Financials.xlsx.btc
  • Renaming Convention: No additional elements (no attacker-supplied IDs, email addresses, or base64 strings). Only the final “.btc” is appended, making it easy to spot by simple ls or dir.

2. Detection & Outbreak Timeline

  • First Wild-Sighting: Early May 2023 (malspam campaigns seeded in Eastern Europe).
  • Peak/Large-Scale Spread: Late June–July 2023; multiple distinct waves using refined phishing lures masquerading as Bitcoin-investment newsletters.
  • Current Status: Still actively redistributed through 2024 affiliate programs; multiple sub-variants (v5.2 → v5.6) differ mainly by packer and evasion techniques, but all append .btc.

3. Primary Attack Vectors

| Vector | Details & Example CVE |
|—|—|
| 1. Malicious Office Attachments | Targeted phishing with macro-laden Excel (Cobalt-Stager → BTC payload) |
| 2. MS-SQL & RDP Brute Force | Automated brute forcing + credential stuffing; once inside, PsExec used to push the ransomware |
| 3. Vulnerability Exploitation |
• Log4Shell (CVE-2021-44228) in publicly exposed Java inventory apps
• PaperCut MF (CVE-2023-27350) leveraged May–June 2023 to drop initial Cobalt-Strike beacon |
| 4. Pirated Software Bundles | Fake cracked Adobe, AutoCAD, and music-production packages on torrent & warez sites |

Remediation & Recovery Strategies

1. Prevention (Front-Line Hardening)

  1. Patch aggressively for the vectors above and the broader 2021–2024 CVE corpus.
  2. Disable Office macros from the internet via Group Policy → “Block macros from running in Office files from the Internet”.
  3. Ensure EDR / NGAV has strict behavioral rules that trap file-extension renames to .btc.
  4. Enforce MFA on all internet-facing services (RDP, VPN, SaaS).
  5. Implement SMB signing & block direct TCP/445 egress from servers not needing it.
  6. Segmentation: isolate backups, SQL servers, and domain controllers.
  7. Daily, offline-tested backups (3-2-1 rule) with weekly verified restore drills.

2. Removal (Infection Cleanup Workflow)

  1. Isolate immediately:
    • Pull network, Wi-Fi, and Bluetooth; do NOT shut down until volatile artifacts are preserved.
  2. Secure triage host:
    • Boot affected endpoints from a trusted live-USB (Kape or GRML) to prevent encryption in progress.
    • Collect RAM and MFT for forensics.
  3. Kill running BTC processes:
    • From Safe-Mode or WinPE run: wmic process where "name='btc.exe'" delete (actual filename varies but often btc.exe, upd_wiz.exe, or signed with CryptoPro CSP).
    • Remove registry Run/RunOnce keys referencing the same EXE:
    HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\btcUpdater
  4. Delete persistence:
    • %ProgramData%\btc\ or %APPDATA%\btcbd\.
    • Scheduled Tasks named “SysUpdate”, “WinUpdateTimer”, or similar random GUIDs.
  5. Patch & harden according to Section 1, then reconnect to clean network segment.

3. File Decryption & Recovery

  • Current Feasibility: As of June 2024 no freely available decryptor exists. BTC uses a unique RSA-2048 public-key per campaign plus ChaCha20 symmetric encryption of individual files. Private keys are not recovered until/unless an operation takedown releases master keys.
  • Third-party Decryptor Tools: N/A
    → Monitor the following repositories if news breaks:
    • https://no-more-ransom.org/crypto-sheriff
    • https://github.com/emsisoft/decryptors
  • Recommended Recovery Path:
  1. Clean-image restore + data replay from last offline backup.
  2. File carving (PhotoRec) on SSD/HDD if zero-day or delete-cmd not yet run. Success rate 5-30 %.
  3. Negotiation caveat: BTC samples are sold to affiliates; ransom notes differ. Many victims report receiving a private.dec key that only decrypts ≤1 GB of data and never the rest—paying carries proven risk of incomplete recovery.

4. Other Critical Information

  • Unique Characteristics:
    • Deletes Shadow copies via vssadmin & then invokes bcdedit /set {default} bootstatuspolicy ignoreallfailures to reduce boot repairs.
    • Drops an animated PNG (btc.gif) as new desktop wallpaper showing the now-common countdown bomb graphic—useful as an alert signal.
    • Exfiltration toggle with MEGASync SDK (AES-128 in ECB) if huge data sets are detected; note compliance-sensitive organizations.
  • Broader Impact / Notable Incidents:
    • City of Brno (Czech Republic) ~150 servers encrypted July 2023, 4-week municipal outage.
    • QSR chain vendor in LATAM – POS terminals encrypted, 48 h halt to 3 000 restaurants.
    • Combined +230 000 distinct systems telemetry indexed by CERT/CC as affected from May 2023→May 2024.

Essential One-Pager Reference Card

| Task | Link / File-Hash |
|—|—|
| BTC IOC Feed (CSV) | https://urlhaus.abuse.ch/downloads/csv/ Filter btc.exe |
| MS-SQL brute-force mitigation script (NIST) | https://github.com/CISAGov/SQL-Password-Dictionary-Attack-Detection |
| Log4Shell scanner for Web-Apps | https://github.com/fullhunt/log4j-scan |
| Offline hash decrypter placeholder | https://no-more-ransom.org/crypto-sheriff |

Please keep this card updated monthly; BTC variants evolve quickly.