b2fr

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files encrypted by B2FR ransomware are universally re-labelled with the suffix .b2fr.
  • Renaming Convention: The malware appends .b2fr as a secondary extension (it is added after the original extension).
  • Example: Quarterly_Report.xlsx becomes Quarterly_Report.xlsx.b2fr.
  • There is no random string or machine ID introduced into the filename itself, which can make identification easier compared to some newer variants.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First telemetry and victim support submissions were noted late February 2025; the campaign gained momentum through March–April 2025.
  • CVE-2017-0144 (EternalBlue) resurgence in compromised MSSQL servers preceded large-scale deployment in mid-March.
  • Public reports and B2FR ransom notes began appearing on malware repositories 24 March 2025.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Remote Desktop Protocol brute-force / compromise: B2FR maintains an internal dictionary of 1.2 million common RDP credentials; once it achieves valid logins, it elevates via Token Impersonation dumps.
  2. EternalBlue (SMBv1 vulnerability, CVE-2017-0144): Re-enabled by misconfigurations on legacy Windows 7/2008 systems.
  3. Phishing Emails: ZIP archives delivered via DocuSign-branded e-mails contain ISO or IMG files (“Invoice_[DATE].img”) that house a signed B2FR loader.
  4. Unpatched MS-SQL servers: Exploits CVE-2021-1636 (SQL RCE) to drop the initial stage; B2FR then propagates laterally via command-and-control scripts.
  5. Software supply-chain abuse: A free photo-editing utility (v3.11) hosted on a developer forum was trojanised with a delayed-execution B2FR dropper.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
  • Disable SMBv1 across the fleet (Group Policy: Computer Configuration → Policies → Administrative Templates → MS Security Guide → “Configure SMBv1 client driver”).
  • Enforce multi-factor authentication (MFA) for all RDP endpoints.
  • Lock down MS-SQL:
    – Disable xp_cmdshell unless strictly required; audit SQL logins weekly.
    – Apply KB5005043SQL (or later cumulative) to close CVE-2021-1636.
  • E-mail filtering: Block ISO / IMG / MSI attachments that originate from external sources (O365 EOP + Defender policies).
  • Network segmentation: Storage VLAN isolated from user subnets; enforce ACLs at L3/L4 to prevent lateral SMB enumeration.
  • Backups: 3-2-1 model with immutable (object-lock) cloud storage and at least one offline / tape copy; test restores weekly, not simply quarterly.

2. Removal

  • Step-by-Step Cleanup:
  1. Immediately isolate: Disconnect NIC, disable Wi-Fi/Bluetooth; snapshot RAM if forensics is planned.
  2. Boot an offline recovery OS (e.g., Kaspersky Rescue Disk 18 or WinPE) to prevent resident encryption service from spawning.
  3. Scan with two engines: ESET 17430+ (detects B2FR.Win32.Filecoder), Bitdefender Ransomware Remediation 4.3.5+.
  4. Locate persistence:
    • Registry: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run → “B2FR-Svc”.
    • Scheduled Task: B2FR_UpdateCheck.
    • Service: ‘B2FR Shell Extension’ (svcHost spoof).
  5. Purge artifacts:

    del /f /s /q C:\Windows\System32\b2svc*
    wevtutil cl System && wevtutil cl Application # optional if logs heavily corrupted
  6. Patch & reboot: Apply MS22-April CU or equivalent OS updates prior to re-storing normal network connectivity.

3. File Decryption & Recovery

  • Recovery Feasibility: Files CANNOT be decrypted without the attacker’s RSA-2048 private key; there is no public decryptor as of 16 April 2025.
  • Essential Tools / Suppliers:
  • Backups ONLY—no flaws discovered in the encryption routine (AES-256-CBC per file + RSA-2048 session keys).
  • If offline backups do not exist, evaluate file-recovery tools for shadow copies: ShadowCopyView or VSSAdmin list shadows (only useful if the malware did not delete them).
  • Maintain and rotate Windows Repository backups (WBAdmin + VSS) to avoid encryption.

4. Other Critical Information

  • Unique Traits:
  • B2FR installs a 7-day countdown timer (replacing the standard wallpaper); after Day 7 the ransom doubles and a mega.nz URL with exfiltrated data is advertised to victims and competitors.
  • Performs double-extortion: Steals browser credentials (via DPAPI changes in v1.2) and screenshots plaintext documents before encryption, pushing them to an attacker-controlled Discord webhook.
  • Uses an uncommon GPG-encrypted bash script on Linux victims (b2fr.sh) for cross-platform volume encryption, making it a flat-rate charge end-to-end across heterogeneous environments.
  • Wider Impact: Close to 180 global organizations reported infections in the early weeks. Two regional hospitals (EU) had to revert to paper records for 4 days; one US county voting registration server was hit, although no ballot data was altered.