birbb

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: birbb – each encrypted file receives the suffix .birbb appended immediately after the original extension.
    Example: Annual_Budget.xlsx.birbb

  • Renaming Convention: The malware preserves the entire original filename and path, only appending .birbb. This is characteristic of Chaos-family derivatives that use single-step renaming instead of full filename hashing, making it easier for victims to deduce which files were affected.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First cluster of sightings posted on BleepingComputer forums and ID-Ransomware uploads began in late October 2024. Activity ramped up through December 2024 and has remained at low-to-moderate levels as of January 2025. It currently appears to be run by a single affiliate, rather than a widespread Ransomware-as-a-Service (RaaS) campaign.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Malicious e-mail attachments – ZIP/RAR archives containing a Windows shortcut (.LNK) that downloads the next-stage loader (birbb.exe). Lures impersonate unpaid invoices, delivery notifications, or donation receipts.
  2. Exploitation of exposed RDP – brute-force attacks against 3389/tcp, followed by manual deployment of birbb.exe via cmd.exe /c with --silent switch.
  3. Fake “Cracked” software – distributed through Discord and Telegram channels offering counterfeit game cheats or pirated utilities (e.g., “Photoshop 2025 activated”).
  4. USB worms – removable drives with hidden Autorun.inf and System32.exe dropper (older Chaos fork reused).

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    • Apply the March 2020 SMB patch (KB4551762) and keep OS fully updated to prevent lateral movement.
    • Block outbound port 445 on edge and host firewalls unless explicitly required.
    • Disable RDP from public Internet or enforce VPN-tunnel-only access + lockout policies.
    • Equip e-mail gateways with strong attachment sandboxing and disable macro execution for files received from outside the organization.
    • Implement application allow-listing (Applocker / Windows Defender ASR rules) to block executables in %AppData%, %Temp%, or removable media.
    • Maintain 3-2-1 backups (three copies, two different media, one off-site/off-line).

2. Removal

  • Infection Cleanup Step-by-Step:
  1. Isolate – disconnect the machine and any mapped shares from the network immediately.
  2. Identify persistence – check Registry Run keys, WMI Event Consumers, Task Scheduler, and Startup folders for entries referencing birbb.exe, Winlog.exe, or random GUID folders underneath %AppData%\Local\Low\.
  3. Boot to Safe Mode + Networking (or remove the disk and attach to a clean workstation).
  4. Run a reputable AV engine or rescue disk with latest Chaos/Chimera signatures – Malwarebytes 4.6+, Sophos Home, or Bitdefender Rescue CD all detect Trojan.GenericKD.70629005 (common signature).
  5. Manually delete leftover binaries and restore default Windows Shadow Copy permissions if they were disabled (common Chaos behavior: vssadmin delete shadows /all).
  6. Once logs show negative hits, change ALL local and domain passwords, paying special attention to service accounts.

3. File Decryption & Recovery

  • Recovery Feasibility: Files encrypted by birbb cannot be decrypted without the attacker’s private key. The variant uses AES-256 in CBC mode with a randomly generated 128-byte key per file, then encrypts that key with a hard-coded RSA-2048 public key.
    Current status: No free decryptor available.
  • Essential Tools:
    • Compile a ransom note fingerprint: look for Restore_My_Files.txt; if the ransom note demands “bring $300 in Bitcoin to …” the campaign is the Chaos fork, implying no working decryptor.
    • Upload one pair (encrypted + original) to ID-Ransomware (https://id-ransomware.malwarehunterteam.com) to confirm variant.
    • Store ransom note & a sample file in case a decryption tool is released later.
    • Use ShadowExplorer / vssadmin list shadows to check for intact Volume Shadow Copies; Chaos sometimes skips them on Windows 11.
    • Leverage file-recovery utilities (Recuva, PhotoRec) to scrape recently deleted plaintext files before they were overwritten.

4. Other Critical Information

  • Unique Characteristics:
    • Extremely small deployment footprint: the payload is compressed via UPX (~300 KB) and shows no GUI.
    • Emoji ransom note: the note ends with the line “Have A Nice Day ►(•̀‿•́)◄” – a rare human-readable marker.
    • Network share “spray”: it simply copies birbb.exe with file-share argument when it finds open SMB, then starts it with PSEXEC. This behavior is primitive but effective on flat networks lacking segmentation.
  • Broader Impact: Although the campaign is still niche, its ties to Chaos open-source code mean copy-cats proliferate quickly. Security teams have reported up to 70 % data recovery when workstations are on Windows 10 22H2 with Controlled Folder Access ON, suggesting that Microsoft’s built-in mitigation has significantly blunted payload damage prior to encryption.

If you have sample ransom notes, file-decrypt pair, or traffic PCAPs, analysts encourage uploading them to ChaosTracker (public Google Drive) to assist reverse-engineering efforts. Collective data may eventually yield a master RSA private key.