bigbobross

[Content by Gemini 2.5]

Technical Breakdown – BIGBOBROSS Ransomware (.bigbobross)

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Victims will notice every affected file ends with the suffix “.bigbobross”.
  • Renaming Convention:
    The malware preserves the original filename and simply appends “.bigbobross”.
    Example:
    • Before: 2024_Q1_Financial_Report.xlsx
    • After: 2024_Q1_Financial_Report.xlsx.bigbobross

2. Detection & Outbreak Timeline

  • Approximate Start Date: First large-scale public reports and honeypot hits appeared mid-November 2023, with a concentrated spike during the week of 12–18 Nov 2023. A smaller re-campaign wave was observed in February 2024.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    • Phishing e-mails containing ISO/IMG or macro-laden Office docs themed around “import tax payment”, “invoice overdue”, etc.
    • Abuse of compromised websites to serve drive-by downloads through fake browser-update pop-ups.
    • RDP brute-force / credential stuffing – rapid, automated attempts against exposed 3389/tcp with subsequently deployed malware via PSExec.
    • Exploitation of the ProxyLogon chain (CVE-2021-26855/CVE-2021-27065) against unpatched Exchange servers to plant webshells, then lateral deployment of the payload.
    • Living-off-the-land techniques: WMI, PowerShell, and Scheduled Tasks to run scripts that download and execute the final encryptor.

Remediation & Recovery Strategies

1. Prevention

  • Proactive Measures:
    ▸ Patch Exchange servers immediately – apply the March 2021 cumulative update or later.
    ▸ Enable MFA on all externally accessible services (RDP, VPN, webmail).
    ▸ Disable SMBv1 (unless legacy systems require it, in which case isolate them).
    ▸ Deploy reputable e-mail filtering (attachment sandboxing + macro blocking).
    ▸ Disable Office macro execution from internet-sourced documents via Group Policy.
    ▸ Segregate backups (immutable / offline WORM, or cloud bucket with versioning).

2. Removal

  1. Isolate the host – disconnect from network, disable Wi-Fi/Bluetooth.
  2. Identify running processes named bobross.exe, bcdedit.exe (used maliciously), or unknown spawn of powershell.exe.
  3. Boot into Safe Mode with Networking or use a trusted offline AV rescue disk (e.g., Kaspersky Rescue Disk 2024).
  4. Delete persistence mechanisms:
    – Scheduled Tasks → Microsoft\Windows\Maintenance\BigBobUpdater
    – Registry → HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\BobSession
    – Startup folder → %APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup\bwrapper.bat
  5. Scan & quarantine the remaining binaries with up-to-date EDR/AV.
  6. After confirmed elimination, re-image the system or perform a clean OS installation for 100 % certainty.

3. File Decryption & Recovery

  • Current Feasibility:
    As of May 2024, there is no publicly available decryptor for BIGBOBROSS. The ransomware uses ChaCha20-Poly1305 encryption keys unique per victim, securely generated on the attacker side.
    • Do NOT rely on supposed decryptors promoted in spam/YouTube comments—they are usually further malware.
    • Recovery path:
    ① Restore from offline / immutable backups (Veeam immutable repositories, Acronis cloud with object-lock, AWS S3 Object Lock + MFA delete).
    ② If backups are unavailable, check Windows Volume Shadow Copies:
    vssadmin list shadows and try ShadowExplorer or wmic shadowcopy call. BIGBOBROSS usually deletes them, but occasionally misses on slower endpoints.
    ③ File-recovery tools such as PhotoRec, R-Studio, or Recuva can sometimes recover non-overwritten Office/OpenDocument files from unallocated clusters with partial data loss.

  • Essential Tools / Patches:
    • Exchange: “Exchange Server Security Updates March 2021” (KB5000871)
    • Windows: “Disable-SMBv1.ps1” Microsoft script + April 2024 cumulative update.
    • Sysmon & Windows Defender ASR rules to block “credential dumping” and “Ransomware behavior”.
    • Free diagnostic utility: Emsisoft Emergency Kit to verify no residual infection before lifting isolation.

4. Other Critical Information

  • Unique Characteristics:
    • Appends the cheekily harmless “.bigbobross” extension and drops a ransom note named README_TO_DECRYPT.txt containing ASCII art of the painter Bob Ross. The threat actors use encrypted protonmail addresses and a Tor chat portal; negotiations are handled manually—there is no dedicated leak site—yet.
    • Uses lightweight GoLang-based dropper (≈3 MB) signed with stolen certificates to evade EDR until final payload detonation.
  • Broader Impact:
    • Primarily impacts small to mid-size businesses across North America and EMEA who lag on Exchange and RDP patching; numerous MSPs, printing services, and healthcare providers have documented incidents.
    • Average ransom demand hovers around 0.55 BTC (~USD 19 k) but negotiators report reductions to 35–40 % upon 10–14 days of silence.
    • Global compliance note: Law-enforcement (CISA, NCSC, BSI) list BIGBOBROSS under the Zeoticus 2.0 cluster, suggesting an affiliate model using leaked Conti-style tooling.
    • Ransomware eradication must be paired with credential hygiene; rotate all privileged credentials on the estate—attackers retain access if not evicted completely.

Deploy these recommendations methodically to reduce attack surface today and to achieve swift, clean recovery tomorrow.