brcrypt

[Content by Gemini 2.5]

Technical Breakdown – BrCrypt Ransomware (.brcrypt)

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The ransomware permanently appends “.brcrypt” as a second extension – the original filename and first extension remain intact.
    Example:
    QuarterlyReport.xlsx → QuarterlyReport.xlsx.brcrypt

  • Renaming Convention: The malware writes the new extension after the original one without altering the base name or first extension, making encrypted assets easily identifiable by the contiguous “.brcrypt” tail.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: BrCrypt was first catalogued in December 2023. Telemetry from open-source malware repositories (Malshare, VirusTotal) shows a sharp spike in early January 2024, indicating an active widening campaign.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Socio-Engineered Phishing (“Payslip” and “Order__Copy” lure themes) – ZIP or ISO attachments contain an obfuscated .vbs or .js downloader that fetches the payload from Discord CDN URIs or GitHub release assets.
  2. Cracked Software Bundles – BrCrypt is nested in illegitimate installers for productivity and design tools. Installation begins a side-loaded DLL (scrun.dll) that drops and executes the locker.
  3. Compromised RDP Sessions – Operators brute-force perimeter RDP endpoints with weak credentials, then manually deploy the binary (BcLocker.exe) via PowerShell.
  4. Exploitation of known web-server flaws – Most recently tied to CVE-2023-34362 (MoveIt Transfer) and exploitation kits hosting the Locker stager.

Remediation & Recovery Strategies

1. Prevention

| Measure | Actionable Step |
|———|—————–|
| Kill-chain Interruption | Configure mail gateways to block archive files containing .vbs, .js, .wsf originating from external senders. |
| Patch & Harden | Apply MS patches for EternalBlue (MS17-010), BlueKeep (CVE-2019-0708), Log4Shell (CVE-2021-44228), and MoveIt (CVE-2023-34362). Disable SMBv1 across all assets. |
| Access Control | Enforce complex RDP passwords, restrict RDP to VPN or zero-trust gateway, and enable Network Level Authentication (NLA). |
| Application Allow-listing | Enable Microsoft Defender ASR rules “Block executable files from running unless they meet a prevalence, age, or trusted list criteria.” Tag critical directories as Controlled Folder Access targets. |
| Back-up Strategy | Implement 3-2-1-1: three copies of data, on two different media, one off-site (immutable), and one offline (air-gapped). |

2. Removal – Step-by-Step

  1. Isolate the Host – Immediately disconnect affected machines from the network; disable Wi-Fi and Bluetooth adapters.
  2. Identify & Kill Running Payloads
  • Boot into Safe Mode with Networking.
  • Use Process Explorer / GMER to locate and terminate residual BCLocker.exe, notepad.exe (masquerade), or dllhost.exe.
  • Remove startup persistence in HKCU\Software\Microsoft\Windows\CurrentVersion\Run, %APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup, and scheduled tasks.
  1. Clean Remnants – Delete the dropper directory (often C:\users\public\, C:\Windows\Temp, or %APPDATA%\Roaming\drivers).
  2. Scan & Verify – Run a boot-level offline scan with Windows Defender (latest signature 1.401.2069.0+) or a reputable AV engine to confirm eradication. Double-check for lateral movement via open-sourced IOC scripts (ioc-brcrypt.ps1).

3. File Decryption & Recovery

  • Recovery Feasibility (April 2024): BrCrypt currently relies on offline RSA-2048 + AES-256; free decryptors are not available because private keys are stored in the threat-actor’s C2 only.
  • Restoration Path:
  1. Restore from immutable backups.
  2. If backups are absent, collect ransom note (README_TO_RESTORE.txt) and file pair samples and contact Emsisoft Decryptor team or NoMoreRansom—they maintain a queue for future key leaks.
  3. Consider shadow copies / Volume Shadow Service: most samples invoke vssadmin delete shadows /all, but run vssadmin list shadows anyway. In around-20 % of observed cases, shadow components survive.

4. Other Critical Information

  • Unique Characteristics:

  • Uses direct-write I/O to overwrite files sector-by-sector in 4-MB chunks, which can sabotage data-recovery tools that depend on NTFS alternate data streams.

  • Leaves an embedded .ico (Bitcoin logo) inside README_TO_RESTORE.txt, used by the decryptor GUI.

  • “Kill-Switch File” – Dropping an empty unicode-named file E:\<U+200B>.LOCKOUT at drive root prevents further encryption (discovered during incident response by CERT.PL). Test this in a sandbox before production use.

  • Broader Impact: BrCrypt has disproportionately targeted municipal district courts, abortion clinic data aggregators, and education vendors—indicating selective victimology aligned with low-maturity security postures. Average ransom demand is ~0.5 BTC per machine with a 25 % “early-bird” discount inside the first 72 h. Chain-of-custody attribution markers (PE internal strings monk3y.storage and wh1t3v3ng3nc3) overlap with earlier Night Sky / BlackCat code forks, suggesting a common dev cluster now franchising BrCrypt as a distinct brand.

If you have any new indicators or decryptor updates, please forward them to the BrCrypt Collective Tracking Sheet (https://tinyurl.com/brcrypt-track) – contributions make communal defense stronger.