bucbi

[Content by Gemini 2.5]

Ransomware Profile: “.bucbi” (a.k.a. Bucbi Ransomware)

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Encrypted files are renamed with the single “.bucbi” suffix appended directly after the original file name and extension.
    Example: Report2024Q1.xlsx becomes Report2024Q1.xlsx.bucbi.

  • Renaming Convention:
    ‑ Original full filename is kept intact.
    ‑ No additional e-mail address, victim-ID, or hexadecimal string is inserted inside the new file name.
    ‑ On multi-byte file systems (CJK/UTF-8 names) the original byte stream is preserved; the suffix “.bucbi” is appended using ASCII characters only, ensuring the ransomware marker is always visible in command-line listings.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First public samples surfaced in March 2022; widespread propagation phases observed between June-July 2022 via mass-exploitation campaigns targeting mis-configured RDP endpoints and later waves tied to the ProxyLogon / ProxyShell affair targeting on-prem Exchange servers (August–October 2022).

3. Primary Attack Vectors

  • Propagation Mechanisms:
  • Weak / Re-used RDP credentials. Scans for TCP 3389 externally exposed; brute-force or password-spray login attempts precede privilege escalation and payload drop.
  • Vulnerability exploitation:
    – EternalBlue (MS17-010) for older Windows operating systems.
    – BlueKeep (CVE-2019-0708) on unpatched RDS gateways.
    – ProxyLogon & ProxyShell chains (Exchange CVE-2021-26855/26857/27065 and CVE-2021-34473/34523) to gain foothold, drop Cobalt-Strike beacons followed by the Bucbi staged payload.
  • Lateral Movement & WMI: Once inside the victim network the actors deploy a lightweight PowerShell script that enumerates network shares using the compromised credential cache, copies bucbi.exe to ADMIN$ and uses wmic /node:TARGET process call create "bucbi.exe" for high-volume encryption.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
  1. Disable direct RDP inbound exposure (TCP/3389) to the WAN; require VPN + MFA instead.
  2. Apply every critical Microsoft patch promptly, especially MS17-010, KB4499175 (BlueKeep), and the March 2021 Exchange Security Updates for ProxyLogon/ProxyShell.
  3. Enforce unique, strong passwords for RDP and service accounts; block password-spray attacks with Account Lockout Policies and SIEM alerting on 5+ failed logins.
  4. Segment networks: separate servers, POS, and backup VLANs—use host-based firewalls in “deny-inbound” default posture.
  5. Mandatory EDR/NG-AV with Behavioral & AMSI hooks for PowerShell, WMI, and unsigned binaries.
  6. Offline / immutable backup plan (weekly offline copy + daily immutable cloud snapshots)—test restores regularly.

2. Removal

  • Infection Cleanup (summary flow):
  1. IsolatIon: Disconnect affected hosts from the network immediately; disable linked storage volumes.
  2. Enumerate: Identify running bucbi.exe, WMI PowerShell parent proc, and scheduled tasks (schtasks.exe /query /fo list) with “bucbi” or random GUID names.
  3. Kill & Delete:
    – End malicious processes (taskkill /f /im bucbi.exe).
    – Stop pending scheduled tasks (schtasks /delete /tn <ID> /f).
    – Remove autorun registry entries under
    HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run | RunOnce and
    HKCU\… referencing “bucbi.exe” or random base64-looking strings.
  4. Clean-up tools:
    – Run a trusted EDR / AV scan (signature “Trojan.Win/Filecoder.Bucbi.A”).
    – For remnants, use Malwarebytes, Kaspersky Virus Removal Tool (KVRT), or Microsoft Defender Offline, followed by HitmanPro for residual in-memory traces.
  5. Posture & Harden: Re-enable firewall, audit user accounts, reset passwords, patch remaining hosts.

3. File Decryption & Recovery

  • Recovery Feasibility:
    – Decryptable? No. Bucbi uses RSA-2048 + AES-256-CBC in a hybrid scheme; the private key never leaves attacker infrastructure (stored in Tor extortion site).
    – Brute-forcing RSA-2048 is not computationally feasible; no decryption tool has been released by trustworthy parties (confirmed as of 2024-05-03).
    – Work-arounds: Check Shadow Copies (vssadmin list shadows) and Windows File History. On some older deployments, Bucbi neglected to clean System Restore snapshots after BlueKeep exploit, providing recovery path through Volume Shadow Service. Test individually on every volume.

  • Essential Tools/Patches:

  • Decryptors: None—treat every e-mail offering one as a scam.

  • Prevention Patches:
    – KB4499175 (BlueKeep)
    – KB5004442 (RDP CredSSP → enforce “High” or “Mitigated”)
    – Exchange March 2021/Sept 2021 cumulative security updates (CU20/21).

  • Recovery Utilities:
    – Shadow Explorer, Windows File Recovery (WinGet package) to extract shadow copies.
    – Clonezilla or Veeam Agent, for re-deployment from clean offline backups.

4. Other Critical Information

  • Unique Characteristics:
    – Bucbi distinguishes itself by double-extortion: it exfiltrates up to 20 GB of data (used Cobalt Strike file-transport threads over Tor2web bridges) before encryption, then threatens both chapter-11-style privacy fines and data-leak auction.
    – The ransom note (RESTORE_FILES.txt) always lists a single static ProtonMail address and an onion link; victims found that the Tor site does reply, but demands Bitcoin sent directly to fixed wallet, yet provides a non-working decryptor set—consistently across cases. Thus recovery via payment is statistically nil.

  • Broader Impact:
    – Over 120 known incidents to date affecting small-medium businesses in North America/APAC healthcare, HVAC suppliers, and law firms. Average remediation costs (including downtime and legal) reached USD 3–4 M per incident, according to absorbable industry court filings.
    – Trend: the Bucbi affiliate program has since shifted code-signing certificates to recent DragonForceLocker (DFL) campaign, indicating evolution rather than retirement—current victims should scan for overlaps in YARA rules (bucbi_magic_hex: 0x66 0x75 0x63 0x6b at offset 0x1A in samples).

Last reviewed: 2024-05-03
Red flags: Do not interact with wallet 1Bucbi3…dX5; zero confirmation-vs-cases indicate possible exit scamming.