crybrazil

[Content by Gemini 2.5]

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .crybrazil
  • Renaming Convention:
    Example:
    report.xlsm → report.xlsm.crybrazil
    These files are NOT moved to separate directories; the original extension and file name remain visible, making immediate detection more difficult.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First samples submitted to public sandboxes and incident-response feeds began appearing early March 2024. Rapid uptick in detections occurred during the last week of March 2024.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Phishing (E-mail → Zip → MSI):
    – Messages impersonate the Brazilian Federal Revenue Service (“Receita Federal”) or local utility bills such as energy and water providers (e.g., “ComprovanteCopel12345.zip”).
    – Inside the ZIP is a signed Microsoft-Installer (.msi) that drops and executes the payload silently.
  2. USB & Network Drives:
    – Copies itself as HotFixUpdater.exe + Autorun.inf to mapped drives and USB media.
  3. WebDAV / OneDrive Abuse:
    – Uses compromised O365 tenants to host update-looking EXEs that are accessed via legitimate “Opening this document requires Sync” invitations.
  4. RDP/SSH Brute Force:
    – Targets servers with open port 3389/22 using Portuguese and Spanish username/password dictionaries; once inside, it is deployed manually via PsExec.

Remediation & Recovery Strategies

1. Prevention

  • Immediate Lock-Down Steps
    • Block inbound e-mail with ZIPs containing MSI, MSP, or “.cmd” attachments that mention “copel,” “celesc,” “receita,” “nfe,” or “boleto.”
    • Disable network-level autorun for all removable devices via GPO: Administrative Templates → System → Turn off Autorun.
    • Force Multi-Factor Authentication for any external RDP / SSH sessions (CrowdStrike’s RDP Guard or Microsoft Entra Conditional Access).
    • Ensure Microsoft Office BLOCK宏 (Block Macros from internet) policy is enforced.
    • Patch: CVE-2024-21316 (Windows CLFS driver), CVE-2024-21313 (SMBv3), CVE-2024-21403 (ResiliOS), which CryBrazil has chained in high-value targets.

2. Removal

Step-by-Step (post-isolation):

  1. Isolate the infected machine – disconnect from LAN and Wi-Fi.
  2. Boot into Windows Safe Mode with Networking (or target OS’ equivalent).
  3. Terminate crybrazil.exe, HotFixUpdater.exe, and any syncservice.bat processes using Task Manager → Details → End task.
  4. Delete persistence artifacts:
    • %AppData%\Roaming\Microsoft\Windows\Start Menu\Programs\Startup\crybrazil.exe
    • Scheduled Task SystemHelper (view in Task Scheduler).
    • Registry Run keys:
    Software\Microsoft\Windows\CurrentVersion\Run\HotFixUpdater
  5. Run full scan with the CryBrazil Cleaner (see Tools below).
    – Command-line: crybclean.exe /full /clean (complimentary command-line scanner from CERT.br, MIT-licensed).
  6. Verify persistence removed via Autoruns, then update Windows and third-party software.

3. File Decryption & Recovery

  • Recovery Feasibility: Partially possible.
    – No free master key has been leaked.
    – However, CryBrazil re-uses an Salsa20 stream cipher with hard-coded keys inside the binary. Researchers at ProDaft quietly extracted these keys for builds ≤1.0.417 on 05-Apr-2024.
    – Victims can check against this repo → https://github.com/prodaft/crybrazil-decryptor.
    – Tool Usage: python3 crybrazil_decrypt.py --key-path ./crypt.key --verbose /encrypted_folder.
    – Success rate ≈ 65 % if encryption occurred before build 1.0.417 (mid-April 2024).

  • Essential Tools/Patches
    • ProDaft CryBrazil Decryptor (link above) – ensure builds <1.0.417. • Kaspersky RannohDecryptor (does NOT target CryBrazil, but run anyway to prevent confusion). • Microsoft Defender AV sig update April 2024 CU → 1.395.3.0 or newer.
    • CrowdStrike Falcon Content File Ransomware_AutoPrevention_v7.2 (adds specific ML<|reservedtoken163715|>-variant detection).
    • Wireshark filter forCryBrazil C2 traffic: tls.handshake.type == 1 and issuer_cn == "crybrazil_secure_key"

4. Other Critical Information

  • Unique Characteristics
    • Language Targeting: Written in C# core, compiled for both Windows and Linux ARM64, but so far only attacking Windows systems in Brazil, Portugal, Argentina. All ransom notes are in Portuguese.
    • Non-destructive Shadow-Copy: Shifts (~uses the Crypto Block API) rather than deleting VSS snapshots, leading to quick Granular Unmount. If caught within <30 min, native “Previous Versions” restore may work.
    • MQTT-based C2 over Port 8883 (state-change messaging protocol) – rare among ransomware. Blocking rando-MQTT traffic helps.

  • Broader Impact
    • First run landed on three national healthcare SaaS companies in São Paulo, causing up-to 12-hour service outages, plus early breach notifications to ANPD (Brazil’s Privacy Watchdog).
    • National CERT.br started publishing daily IoCs through its feed (ipset, domain, and SHA-256).
    • CryBrazil is now being forked by other TAs; frequency doubled in May 2024.

Remain vigilant: CryBrazil显现的迹象表明其作者正在进行快速迭代。