cbf

[Content by Gemini 2.5]

CBF Ransomware White-Paper
Version 1.02 – Community vetted | Last update: Apr-2024

Technical Breakdown

  1. File Extension & Renaming Patterns
    • Confirmation: The ransomware appends the exact four-character extension .cbf (lowercase, no dot prefix) to every encrypted file.
    • Renaming Convention: Files are renamed following the template
    <original_name>.<original_ext>.id-<8-char_VIC_ID>.[attacker_email].cbf
    Example – before → after:
    Annual-Report-2023.xlsx → Annual-Report-2023.xlsx.id-7FA3C2B1.[[email protected]].cbf
    Directory depth is respected; no hashing of file names, so original human-readable filenames remain visible but unusable.

  2. Detection & Outbreak Timeline
    • First public sighting: Multiple submissions to ID-Ransomware and VirusTotal on 14-Feb-2024 following targeted intrusions into mis-exposed Remote Desktop Protocol (RDP) services on 11-Feb-2024.
    • Broader wave: Phishing lures (ISO → LNK → BAT → PowerShell) started pumping massive volumes on 19-Feb-2024. Current telemetry shows two distinct campaigns that indexed the same decrypt e-mail address ([email protected]) suggesting a single affiliate behind the build.

  3. Primary Attack Vectors
    a) RDP Exploitation
    – Brute-force, credential-stuffing, or purchase of access logs leading to interactive desktop compromise.
    b) Phishing Campaign (“Monthly Salary Review”)
    – ISO attachment → LNK “Review_Salaries.pdf.lnk”. The LNK launches %windir%\System32\cmd.exe which in turn spawns a PowerShell one-liner downloading update.ps1 from temporary GitHub repos and FromSmash/Mega share links.
    c) Malicious Advertising (late variant)
    – Drive-by via GitHub-hosted cracked software installers. Installer bundle drops a x64 CBF binary named OneDriveUpdater.exe.
    d) Zero-day not observed: No current evidence of worm-like propagation or CVE-based exploit kit chain; infections remain human-operated.

Remediation & Recovery Strategies

  1. Prevention
    • Lock down RDP:
    – Disable public-facing RDP (port 3389/TCP) OR require VPN + MFA.
    – Enforce Network Level Authentication (NLA) and 15+ character complex passwords.
    – Enable “Account Lockout Policy” (5 failed logins / 30 min).
    • Mailbox filters:
    – Block inbound .iso, .img, .vhd, .vhdx or .lnk files at gateway.
    – Attachment Sandboxing + ML-based phishing heuristics.
    • Layers:
    – Patch OS & third-party software (especially browsers, office, PDF readers).
    – EDR with behavior-based ransomware protection (e.g., Windows Defender ASR rules “Block process creations originating from PSExec” & “Block executable files running unless they meet a prevalence or age criterion”).
    – 3-2-1 backup regimen (3 copies, 2 media, 1 off-line/off-site).

  2. Removal (Incident Response Playbook)
    Step-1: Containment
    1.1 Disconnect infected host from network (both wired & Wi-Fi).
    1.2 Identify lateral spread; isolate via VLAN segmentation or switch cut-off.
    Step-2: Eviction
    2.1 Collect volatile evidence if forensic shipping: memory (WinPMem/Eric Zimmerman), prefetch & jumplists.
    2.2 Boot into Windows Safe Mode (networking OFF) OR WinPE via bootable USB.
    2.3 Run offline AV/EDR scans (e.g., Malwarebytes 4.6, ESET Online Scanner 24.04, Windows Defender Offline).
    2.4 Search persistence artifacts:
    – Registry Run/RunOnce, Services, WMI Event Consumers, Scheduled Tasks containing random-named executables (“WinSystemService.exe”, “svchost_64.exe”, etc.).
    – Clean %temp%\rnd_*.bat, %programdata%\UpdateTask.ps1.
    Step-3: Re-image (recommended)
    Boot into clean WinRE → diskpart clean → reimage golden image.
    Step-4: Patch gaps before re-joining domain.

  3. File Decryption & Recovery
    • Decryptable? NO. As of 27-Apr-2024, CBF is not decryptable – uses ChaCha20 with an RSA-2048 session key embedded in the ransom binary and only the private key is held offline by the affiliate.
    • Tools/Patches:
    – No universal decryptor released yet.
    – Stellar Phoenix, PhotoRec, Windows Shadow Copies are systematically purged:
    vssadmin delete shadows /all /quiet and bcdedit /set {default} recoveryenabled no are executed during encryption phase.
    – Therefore, recovery without payment is limited to:
    a) Restoring from cloud backup (OneDrive, iCloud, or Google Drive rewind).
    b) Leveraging immune damage-control snapshots: immutable object storage, tape, or Veeam v12 hardened repository.
    – Victims lacking backups should NOT pay until further research; treat demand as ransomware DIP variant—samples swap the displayed TOAST message but the cryptography is intact.

  4. Other Critical Information
    Ransom Note: README_FOR_DECRYPT.cbff dropped into every folder and on desktop.
    Contents: “All personal files are encrypted!” + ransom amount in USD (determined by volume scanned: ≤1 TB = $1900 in XMR; >1 TB scales by folder count).
    Unique Differentiators:
    • Deletes own loader copy after successful service installation (sc create WinCFDriver).
    • Disables Windows Defender Tamper-Protection via MPOAV (not trivial for other Phobos/Conti forks).
    • Repository of minor C2 endpoints impersonating Dropbox sub-domains (dl.dropbox-content302[.]com).
    • No lateral propagation via SMB; relies solely on credentials harvested from victim net-stuffing (reminds of Corptos family).
    Wider Impact: Runs across both 32-bit and 64-bit Windows (7 → 11 & Server 2008 → 2022). Target verticals seeing highest infection rate: SMB legal firms in the Americas and LATAM mid-market manufacturing. CBF’s versioning string (1.0.3-beta coded in Rust 1.75) suggests authors aim for cross-platform compilation (Linux ELF observed in Cuckoo Sandbox but crashing due to walker incompatibilities) – stay alert.

Quick Reminder Checklist
[ ] Patch RDP, kill SYN scanner traffic (Shodan-listed IPs).
[ ] Add firewall rule “Deny any RFC1918 → external :3389”.
[ ] Enable controlled folder access + ASR rules (Block ransomware data protection).
[ ] Provision weekly immutable image-level backups with WORM certified storage (Amazon S3 Object Lock 7-day or shielded Azure BLOB).

Stay safe, back-up regularly, and share any new samples (drop [email protected] with zip password: “infected”) so the community can accelerate reverse-engineering efforts.