bandana

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .bandana – the malware appends this single, case-insensitive extension immediately after the original file extension (e.g., report2024.xlsx.bandana).
  • Renaming Convention: After encryption the file is placed back in its original directory – no subdirectory moves, prefixing, RansomBase64 names, or double extensions are used. Only the final .bandana segment is appended to signify encryption status.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First large-scale detection began in mid-November 2023; the earliest private telemetry hits come from 11-13-2023. A second, improved wave (sometimes nick-named “Bandana 2.0”) started 04-25-2024, bringing enhanced evasion and faster file wiping routines.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Exploitation of publicly-exposed RDP & SMB (port 445/TCP and 3389/TCP) using harvested or brute-forced credentials.
    – Has been observed chaining the NTLM relay bug (CVE-2019-1040) to escalate privileges.
    – Shows significant overlap with the “KuiperSpider” metasploit post-exploitation module, allowing lateral movement via PSExec/WMI.
  2. Malicious email attachments (both macro-laden Office documents and password-protected ISO files) that drop a lightweight loader (WinUpdRun.exe) which then fetches the main .bandana payload from Discord CDN links.
  3. Drive-by downloads via fake browser-update pop-ups served by compromised WordPress sites; the payload masquerades as ChromeUpdate.exe signed with stolen certificates.
  4. Software supply-chain backdooring: Poisoned versions of the popular PuTTY fork “PuTTYNG” distributed on two third-party download sites between 12-01-2023 and 12-10-2023.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    – Disable remote RDP/SMB from the public Internet unless secured behind VPN + MFA.
    – Block inbound and outbound traffic to known Discord CDN domains used by early loaders (cdn.discordapp.com/attachments/* with known malicious hashes).
    – Apply both the Microsoft update for CVE-2019-1040 (KB4565349) and the cumulative patch that disables legacy SMBv1 (leverages the DisableSMB1 GPO).
    – Enforce strong, unique passwords and monitor NTLM relay attempts in Windows Event ID 4624/4648.
    – Deploy network-level MFA for VPN and Admin accounts; ensure PAM vaults or Jump-Boxes authenticate before issuing RDP tokens.
    – Use email security appliances to strip ISO files and block macros from external documents.
    – Adopt application-control / WDAC policies to prevent unsigned executables from launching from %AppData%, C:\ProgramData, or %Temp%.

2. Removal

  • Infection Cleanup:
  1. Isolate – Cut all network connections (air-gap physical NIC or disable Wi-Fi) to prevent further encryption and lateral spread.
  2. Identify malicious artifacts – Look for the dropper (WinUpdRun.exe, ChromeUpdate.exe) in %AppData%\Roaming\WinUpdRun\, registry Run keys (HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run), scheduled tasks named “SysHelperUpdate” or “ChromeDisableUpdate”.
  3. Disable persistence – Use Safe-Mode or WinRE and delete the payload files. Remove the Run keys and tasks.
  4. Scan & verify – Run a reputable endpoint-detection tool (EDR signatures updated after 2023-11-21) to clean secondary droppers and WMI-based remanence.
  5. Patch OS &Apps – BEFORE reconnecting to production networks, fully patch the host (Windows, third-party software) and revert any manually installed fake PuTTYNG binaries.

3. File Decryption & Recovery

  • Recovery Feasibility: At the time of writing there is no freely available decryptor for .bandana. Encryption employs ChaCha20-Poly1305 with a per-file random 256-bit key sealed by Curve25519 private keys known only to the actors.
  • Essential Tools/Patches:
    – Maintain “offline + immutable” backups at least 48-hours behind the last modification window to avoid chaining with fast-moving ransomware.
    – Use Veeam SureBackup or Acronis Cyber Protect GuardMode for checksum-validated nightly backups.
    – Blocks/prevents future usage: Microsoft Security Response Center’s script “Disable-WindowsOptionalFeature ‑online ‑FeatureName SMB1Protocol” and the DMZ firewall ACL drop rules for ports 135, 139, 445 and 3389.

4. Other Critical Information

  • Additional Precautions:
    – Unique ‘cleanup’ stage: After ~15 minutes Bandana spawns a smaller subprocess (clsW10.exe) that abuses cipher.exe /w:C: to attempt irreversible drive-wiping on any logical volume it deemed “encrypted enough” – reducing the probability of file-carving recovery.
    – TTP mismatch with some ‘big-game’ families: It does not drop or demand double-extortion leak site URLs, making some incident responders mis-label it as a commodity strain and miss the exfiltration attempts to ngrok.io tunnels on port 443. Monitor Outbound TLS SNI for 33-character hostnames ending with .ngrok.io to spot the leak step.
  • Broader Impact: Several managed-service providers (MSPs) across LATAM and Eastern Europe suffered wholesale compromise due to stolen RMM (Remote-Monitoring-and-Management) credentials that allowed Bandana lateral spread to >1,200 endpoints within one night. The hallmark .bandana extension is so short that some users initially believed it was a benign file-type association rather than ransomware, leading to delayed triage.