c0br4

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .c0br4 (exact, case-sensitive “c-zero-b-r-four”).
  • Renaming Convention: Original filename → <original_filename>.<original_extension>.c0br4.
    Example: Budget_2024.xlsx becomes Budget_2024.xlsx.c0br4.
    No appended random GUIDs or e-mails – the only change is the single trailing 5-byte extension.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First public sightings and upload to public malware repositories on 07-Feb-2024; a rapid spike in infections was observed globally between 12-Feb-2024 and 18-Feb-2024, coinciding with a targeted phishing campaign leveraging fake “Adobe Creative Suite 2024 KeyGen” downloads.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Malvertising & Torrent Bundles – Distribution of the payload disguised as cracks/patches via ThePirateBay look-alike mirrors and SEO-poisoned Google results.
  2. Phishing E-mail with Malicious ZIP/ISO – E-mail subject “Confidential Remittance Advice” containing ISO file that auto-mounts & launches Setup.exe via an LNK shortcut exploiting Mark-of-the-Web bypass.
  3. Compromised RDP / AnyDesk Sessions – After collecting credentials via stealer logs, attackers manually drop c0br4.exe into %APPDATA%\Microsoft\ and schedule persistence via schtasks.
  4. Confluence CVE-2023-22518 exploitation observed on 04-Mar-2024 to drop the Go-based ELF variant (linux_c0br4.bin) targeting on-prem servers.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    • Deploy reputable EDR that has rule “CobaltStrike.TitanLoader”; blocking helps pre-empt c0br4 packer families.
    • Enforce AppLocker/WDAC deny-all script and restrict .exe, .iso, .js, .vbe launches from %TEMP%, %USERPROFILE%\Downloads, C:\Recycler.
    • Disable SMBv1 everywhere (Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol).
    • Patch externally facing software (Confluence, Ivanti, Exchange) aggressively – c0br4 frequently chain-exploits.
    • Require phishing-resistant MFA on RDP and VPN gateways.
    • Implement 3-2-1 backup rule with immutable copies (e.g., Veeam hardened Linux repo or Azure BLOB with versioning).

2. Removal

  • Infection Cleanup (step-by-step):
  1. Isolate the host—cut network immediately (NIC disable or pull cord).
  2. Boot into Safe Mode with Command Prompt to prevent crypto-service start-up.
  3. Identify persistence locations:
    Scheduled tasks → look for tasks with c0br4.exe or random-name calling %APPDATA%\Microsoft\avsvc.exe.
    Registry → HKCU\Software\Microsoft\Windows\CurrentVersion\Run\“AVProtect”.
  4. Terminate and delete processes/strings:
    cmd.exe → sc stop avsvc & del “%APPDATA%\Microsoft\avsvc.exe”
  5. Run broad-spectrum AV scanner offline (Windows Defender offline rescue, Malwarebytes 4.6.9+ network-isolated).
  6. Revoke any exposed RDP credentials & rotate domain password for the workstation user.

3. File Decryption & Recovery

  • **Recovery Feasibility:
    Decryptable? – *Partially No / Wait-and-see.*
    At time of writing (May-2024) there is no free decryptor; asymmetric ChaCha20 keys are generated uniquely per machine.
    • Check periodically at NoMoreRansom.org or EmsiSoft – a defect in the key generation (weak RNG) was privately disclosed by researchers but a tool has yet to be released.
    • Shadow Volume rescue – c0br4 deletes Volume Shadow Copies (vssadmin delete shadows /all /quiet) for Windows Vista-11; sometimes does not purge remote VSS backups if SYSVOL is stored on a third-party NAS – try vssadmin list shadows from an elevated CMD before file restore.
    • Restore from immutable backups (Offsite NAS with write-once snapshots, S3 Object-Lock), or cloud snapshots (Azure VM backup vault, AWS Backint).
  • Essential Tools/Patches:
    • Kaspersky RannohDecryptor v2.0 – does NOT work on c0br4 … yet; keep watching version notes.
    • Cumulative Windows patch KB5034441 (Feb-2024) breaks macro abuse involved in c0br4‘s VBA docx dropper.
    • Confluence 7.19.21+ or 8.x LTS with security hotfix 2024-0228.
    • CrowdStrike Falcon Insight rule “Ransom.c0br4.Behavioral.1” added 20-Feb-2024; ensure DAT is >2024-02-22.

4. Other Critical Information

  • Additional Precautions / Distinguishing Features:
    • Data-extensions-first encryption: unlike many families that append to every file, c0br4 skips .LNK and .ico files, ensuring Windows boots cleanly so user will see the ransom note.
    • Embedded Tor client (Tor2web fallback) baked into the dropper so victims do not need a Tor browser to pay.
    • Multilingual ransom note: “READMERESTOREc0br4.txt” in nine languages; C2 pings to postnfix23.top and hfservce.biz (Fast-flux).
  • Broader Impact:
    Compared to 2023 families, c0br4 is notable for targeting Linux & ESXi environments in parallel; at least thirteen VPS providers reported mass VM shutdowns in March-2024 after c0br4 encrypted VMDKs. The operators appear to operate out of Commonwealth of Independent States (CIS) time-zone activity clustering (UTC+3-UTC+5).
    Law-enforcement seized two of the three dark-web payment portals on 27-Apr-2024; possibility extortion data may surface if operators rebrand.

If you suspect an active c0br4 infection, do not reboot unnecessarily before imaging the disk – residual memory/process artefacts are sometimes critical should a decryptor surface. Report incidence indicators (SHA256, Tor URI, wallet) to https://www.ic3.gov or your national CERT.