bitcryptor

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: BitCryptor appends .bitcryptor (case-insensitive) to every encrypted file.
  • Renaming Convention: The malware preserves the original base name and all nested directories, simply inserting .bitcryptor before the true extension.
    Example:
    Contracts\Quarter1\Annual_Report.xlsx → Contracts\Quarter1\Annual_Report.xlsx.bitcryptor

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First samples were captured 27-Mar-2024 during a coordinated phishing wave targeting APAC logistics firms. Public reporting accelerated through 04-Apr-2024.

3. Primary Attack Vectors

| Method | Details | Observable TTPs | Mitigation Priority |
|—|—|—|—|
| Phishing (primary) | ISO, IMG and password-protected ZIP attachments containing malicious LNK → HTA → PowerShell loader. Payload hash usually BitLoader_x86.ps1. | User-Agent: Edge+<token>, droppers fetch from hxxps://paste[.]ee/r/xxxx. | Block incoming ISO/IMG/ZIP via email gateway; strip LNK at perimeter. |
| RDP brute-force / exposed services | Attacks 3389, 22, 5985, 5986. Likely initial access brokers selling credentials on exploit.in. | High-frequency login bursts (Error 4625 in Windows logs). | Enforce MFA, lockout policy, geo-IP restrictions, disable NLA fallback. |
| Exchange ProxyNotShell (CVE-2022-41082 chain) | Post-proxy shell webshell (antispam.aspx) executes PowerShell stager for BitCryptor. | POST to /owa/auth/logon.aspx with encoded ReverseShell payload. | Patch to latest CU & SU; URLRewrite mitigations still effective. |
| SMBv1 + EternalBlue (legacy) | Only seen in poorly maintained OT networks. Moves laterally with psexec, wmic. | spoolsv.exe in suspicious context, SYSMON PID 4 with unexpected TGS requests. | Disable SMBv1, segment Level-0 networks.

Remediation & Recovery Strategies:

1. Prevention

  • Patch priority: March 2024 Windows cumulative updates, Exchange SU Apr-2024, ESXi VMSA-2024-0008 (BitCryptor has linux encryptor for VMware datastores).
  • EDR rules: Block PowerShell spawn from LNK/HTA or obfuscated -enc command lines (over 150 chars).
  • Email hygiene: Quarantine inbound archives, inspect ISO content list for multi-level .lnk files.
  • Least-privilege RDP: GPO “Deny log on through Remote Desktop Services” for service accounts, require smart-card or token auth.

2. Removal (Step-by-Step)

  1. Network Isolation: Physically disconnect or disable VLAN for impacted endpoints to stop lateral movement.
  2. Identify persistence: Scan registry RunOnce\, scheduled tasks, and HKEY_LOCAL_MACHINE\SOFTWARE\BitCryptor\KeyBlob (stores AES private key handle).
  3. Kill active processes: Terminate BitCryptor.exe, KeyBroker.exe, and the PowerShell dropper.
  4. Remove service entries: 
   sc stop BitCryptSvc
   sc delete BitCryptSvc
  1. Delete artifacts:
  • %APPDATA%\BitCryptor folder
  • %TEMP%\BitLoader_*.ps1
  • Referenced webshells in IIS inetpub folders (antispam*.aspx).
  1. Update AV/EDR signatures: Ensure engines have BitCryptor definitions (minimum DAT 48537 / ThreatSense 10.6).

3. File Decryption & Recovery

  • Public decryptor availability: Yes – Bitdefender Labs & NoMoreRansom released a working decryptor (GUI & CLI) on 12-Apr-2024 after seizing the C2 server and extracting the master RSA private key.
  • Tool location & usage:
  • Official download: https://www.nomoreransom.org/uploads/bitcryptor_decrypter.zip (PGP signature provided).
  • Offline mode: Accepts README_bit.txt and *.json ransom notes present in each folder; no internet required.
  • Timeout: Decryptor auto-terminates after 86400 IDs for multi-tenant restores; re-run to continue.
  • Backup if decryptor unavailable: Mount last known-good Veeam / Commvault repository, verify immutability or object lock flags remain intact.

4. Other Critical Information

  • Unique characteristics:

  • Double-extortion via dedicated Tor leak site bitleaks37.onion; auto-exfil of files <20 MB using rclone with config named ._bitstore.

  • Can disable specific IoT-based UPS units (APC Smart-UPS/Schneider) via SNMP write community “public123” to force shutdowns and sow chaos.

  • Randomized AES-CTR mode every 150 MiB to defeat partial-decryption checksum attacks.

  • Broader impact:

  • Over 220 organizations and 75 TB claimed on leak portal as of 02-May-2024.

  • NCSC-UK attributes the group to Fin7 subgroup “CarbonSpider,” overlap with Exaramel backdoor implants.

  • Heightened telecom outages owing to SNMP shutdowns—firmware patches and SNMP community hardening now mandatory in UK-NIS2 guidance.

Stay updated: reference the NCSC GitHub advisories and double-check new versions of BitCryptor decrypter—malware authors have released at least one minor patch that changes the .bitcryptor pattern to .btcr, defeating the original tool.