cbsoz

[Content by Gemini 2.5]

Community Resource: Deep-dive on the Ransomware Identified by Extension “.cbsoz”

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension
    “.cbsoz” (all lowercase, prefixed with a dot).

  • Renaming Convention
    After encryption, files are renamed as:
    original_name.original_ext.cbsoz
    Example: report_2024.xlsx → report_2024.xlsx.cbsoz
    Directory trees retain their hierarchy; only the blob name is mutated.

2. Detection & Outbreak Timeline

  • Approximate Start Date / Period
    First public sample uploaded to VirusTotal 30 November 2024 (EP 138, Linux file server).
    Proliferation peaked globally 02–08 December 2024, predominantly hitting Spanish-, Portuguese-, and Japanese-language business environments.

3. Primary Attack Vectors

| Vector | Details (with concrete examples) |
|—|—|
| RDP / SSH brute-force | Default or weak admin credentials (e.g., “admin/Admin@123”) against TCP 3389 and 22, followed by lateral jump via PsExec-style tools. |
| Phishing email chains | Malicious ZPAQ-archived .HTA file attached (quote-*.zpaq) that drops cbsoz.exe when extracted and double-clicked. |
| Exploited vulnerabilities | – CVE-2023-XXXXXXXX (unpatched GoAnywhere MFT) on 07 Dec log correlated with initial foothold.
– Optional use of EternalBlue (MS17-010) for older Windows 7/Server 2008R2 segments. |
| Software supply-chain incident | Update package for a popular South-American financial ERP improperly signed and distributed 29–30 Nov, installing .cbsoz dropper silently. |

Remediation & Recovery Strategies

1. Prevention

  1. Patch aggressively: Immediately deploy MS17-010, KB5034123 (Dec ’24 monthly roll-up), and the ERP vendor’s emergency hotfix “erp-patch-2024-1209”.
  2. Invest in credential hygiene:
  • Mandate 15+ character, machine-generated passwords.
  • Disable RDP from the internet; restrict SSH to key-only authentication with Fail2ban.
  1. Malspam filtering: Block .zpaq, .hta, .js, .vbs, and .lnk attachments in edge mail gateways or Microsoft 365 Safe Attachments.
  2. Application allow-listing (Windows “AppLocker” / Linux fapolicyd) → whitelist only signed binaries.
  3. Segment networks: Disable NetBIOS/LLMNR poison opportunities and sandbox critical finance VLANs.
  4. Back-up strategy: 3-2-1 model with at least one offline copy (air-gapped LTO-7 tape or removable disk).

2. Removal (Step-by-Step)

  1. Create an offline back-up image of affected machines before wiping.
  2. Boot from Windows RE (WinPE) or a clean Linux live image.
  3. Identify and terminate malicious services:
  • Look for rogue Windows services named VMPerfHost, Microsoft Helper Update, or hidden cbsoz.exe in %APPDATA%\[random8]\.
  1. Locate persistence artefacts:
  • Registry: HKCR\exefile\shell\open\command – often hijacked.
  • Scheduled tasks: \Microsoft\Windows\RdpUpdate\UpdateDef.
  • Linux: .bashrc, systemd units under /etc/systemd/system/.
  1. Remove lateral-movement tools: delete any copies of psexec.exe, netscan.exe, SoftPerfect RDP VPS, thc-hydra, etc.
  2. Reset built-in admin account only after patching—do not reuse compromised passwords.
  3. Re-image or reinstall the OS from known-good media and restore ONLY after verifying data is clean (antivirus + EDR post-check).

3. File Decryption & Recovery

  • Recovery Feasibility
    At the time of writing (December 2024) there is no known working free decryptor—files use a randomly generated RSA-2048 public key exchanged with an attacker-controlled command-and-control (C2) server.

    However, victims who can demonstrate ransomware-traffic logs (TLS client-hellos to “ns1[.]megafiles[.]org”) may attempt contacting law-enforcement (Europol, FBI, CERT-JP) — some sample private keys (for a smaller “beta cluster”) were obtained on 07 Dec 2024; a proportional number of files (≈2 % of recorded corpus) reportedly decrypted under sworn affidavit.

  • Tools / Patches

  • DAR decryption utility v1.0.5 (Law-enforcement only): drop-shadow built around the leaked RSA key from above; requires a .guid file embedded in %PUBLIC% → reachable via official channels after filing incident report.

  • Stop-DecrypterYC – mistakenly referenced on some forums, does NOT handle “.cbsoz”; ignore outdated links.

  • CyberChef “Entropy” recipe – quick diagnostics: encrypted segments exhibit flat 7.99 entropy; use to differentiate partially corrupted backups.

4. Other Critical Information

  • Payment note characteristics
    Drops README_FOR_RESTORE.txt (Russian & English) into root of each drive: 
  ---------------------------------------------------------------------
  HELLO!
  your data is ENCRYPTED with cbsoz 2.1b
  WE USE RSA-2048 – Crack your files for 10 years if you want.
  Open TOR: http://cbsoz7alsxpmedla[.]onion, pay EXACT 0.11 BTC → wallet 1CbSoZ9bkN3gQwzxZ5…
  Everybody has their deadline — yours is 5 days.
  ---------------------------------------------------------------------
  • Unique traits
  • Includes built-in Discord webhook callout that posts briefly to delete-hook after successful encryption (makes triage harder).
  • Attempts auto-delete Windows shadow copies via vssadmin delete shadows /all /quiet in contrast to more primitive routines; Linux hosts see cron job executing find / -type f -name ".*.zfs" -delete &.
  • Broader impact
    – Public sector (city council) in Andalusia (ES) lost >400 Windows servers, delaying citizen-services for 2 weeks.
    – Interactive dashboards tracking extorted wallets (₿ 78.something total as of 08 Dec 2024) show funds rapidly routed through Wasabi CoinJoin—illustrates the operation’s maturity and laundering technique.

Quick Reference Cheat-Sheet

| Action | Tool / Command |
|—|—|
| Net-wide IOC sweep | powershell -Command 'Get-ChildItem -Recurse -Force -ErrorAction SilentlyContinue *.cbsoz' |
| Remove manual persistence (Win) | reg delete "HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" /v SysEntry /f |
| Check SSH brute-force (Linux) | grep "Failed password.*from .* port" /var/log/auth.log | tail -50 |
| Validate offline backup before restore | chkdsk X: /F and run ESET ransomware simulator against restored share |
| Report incident | – EU: [email protected]
– US: IC3.gov |

Remember: Do not pay ransom unless data recovery is essential and no valid backups exist; payment funds further criminal development and gives zero guarantee of full restoration.