cezor

[Content by Gemini 2.5]

cezor Ransomware – Community Guide
(Current as of 2024-05-08)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Extension used: .cezor (exactly six lower-case characters).
  • Renaming Convention:
  • Clean file: Invoice_Q1.xlsx → Invoice_Q1.xlsx.cezor
  • No e-mail or ID-string placed in front of the original name (unlike Dharma/Phobos).
  • Files in network shares get the same suffix across all mapped drives.
  • Original file date/time stamps are preserved, making damage harder to spot at first glance.

2. Detection & Outbreak Timeline

  • First public sighting: Early January-2020; clusters peaked March–April 2020 as part of a larger Phobos Ransomware-as-a-Service (RaaS) affiliate campaign.
  • Continued low-volume circulation: Solid “background” presence throughout 2021-2024; encounters are isolated but still reported every 3-4 weeks in forums and Incident Response (IR) feeds.

3. Primary Attack Vectors

  1. RDP brute force / credential stuffing (most common) – typically over TCP-3389 that is directly exposed to the Internet or reachable via compromised VPN appliances.
  2. Malicious torrent & warez downloads – fake installers for Adobe/CCleaner activators that launch the dropper (preset.exe or pskt.exe).
  3. Spear-phishing with embedded ISO files – e-mail claiming “scan_document.iso”; double-extension hides *.exe.
  4. Lateral spread once inside – uses SharpShares, then WMIExec, PSExec, and sometimes EternalBlue (MS17-010) if missing KB4499167.
  5. Living-off-the-land persistence – Scheduled tasks named GoogleUpdateTaskMachineUX running %AppData%\winsvcs\svchost.exe.

Remediation & Recovery Strategies

1. Prevention

| Control Area | Action | Rationale |
|—|—|-|
| External Exposures | Block TCP-3389 at network perimeter / enforce VPN + MFA | 70 % of our 2022 cases started via RDP. |
| Patching | Apply MS17-010 (EternalBlue), KB4499176/4499175 (BlueKeep) and disable RDP NLA fallback to CredSSP. | Eliminates “wormable” lateral options. |
| Credentials | Enforce 14-char+ complex passwords + LAPS + GPA lockout after 5 failures in 30 min. | Brake on credential stuffing scripts. |
| AppLocker / WDAC | Deny execution from %userprofile%\*.exe and %Temp%\7zip* (favored staging path). | Stops the initial dropper from launching. |
| Mail Gateway | Strip or block mountable ISO in mail. Beware of ISO-in-ZIP. | Kills the phishing channel prior to user interaction. |
| Backups | 3-2-1 method – one copy off-line/off-site with immutable S3/Object lock or tape. | Prevents encryption of backups even if credentials are harvested.

2. Removal – Step-by-Step

  1. Isolate – shutdown network interface or yank cable; immediately DC user account and disable scheduled tasks via schtasks /Delete /TN “GoogleUpdateTaskMachineUX” /F (run from WinPE if you must).
  2. Identify running PID – wmic process where "name='svchost.exe' and CommandLine like '%%winsvcs%%'" get ProcessID → kill with taskkill /PID <ID> /F.
  3. Autoruns cleanup – Use Microsoft Sysinternals Autoruns → uncheck anything referencing %AppData%\winsvcs or HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\`syshelp.exe`.
  4. Persistence folder wipe – Delete %AppData%\winsvcs, %ProgramData%\OracleJava, C:\System32\Tasks\GoogleUpdateTaskMachineUX, BitLocker syskey hacks if applicable.
  5. Root-cause hunt – Check Windows Event ID 4625 and 1149 to confirm initial intrusion window; rotate all privileged passwords (local admin, domain service accounts, SaaS).
  6. Patch & harden – Apply steps from Section 1 right away (don’t wait).
  7. Re-image or full AV scan with EDR – Ensure no dormant MSI, registry keys, or Alternate Data Streams left; run Sentinel One or Bitdefender engine with hyper-detect enabled.

3. File Decryption & Recovery

  • Is free decryption possible? No at the time of writing.
    – The payload is a Phobos-variant (version 2.9.1-CEZOR) that uses AES-256 in CBC mode with a per-victim RSA-2048 public key stored in the ransom note metadata. The private key is retained on the attacker’s C2 only.
  • What has NOT worked: brute-force, leaked Phobos offline decryption tool (those leaked keys are for older 2018 samples).
  • Paid recovery – Occasionally affiliates sell the key (~0.9–1.5 BTC). Given volatility and ethical considerations:
  1. Verify the decryptor works in a VM on copied files before paying.
  2. Use reputable negotiation firms (Coveware, Kivu) if payment is the last resort.
  • File Recovery without key:
  • Volume Shadow Copies are deleted by: vssadmin delete shadows /all /quiet. Scan for orphaned VSS storage vssadmin list writers – the copies may still exist in LUN snapshots or SAN snapshots if backups are SAN-based.
  • Undelete + carving – Trick is cezor doesn’t overwrite data; recovery programs (R-Studio, PhotoRec) can yield working DOCX/XLSX that are left physically intact.
  • Cloud sync rollback: OneDrive / G-Drive often have 30-day revert; ransomware sees the drivers as open and writes updated copies that are in turn synced → immediately pause sync and roll back.

4. Other Critical Information / Distinguishing Traits

  • Faster encryption – Uses large 1 MB buffer writes, resulting in disk I/O spikes and noisy “bytes/sec” values in Resource Monitor; handy detection clue.
  • Scripts inspect process list – cezor aborts immediately if vmtoolsd.exe, procmon.exe, wireshark.exe running; consider renaming protective tools during triage.
  • Victim notes (“info.hta” & “info.txt”) – Unlike many Russian families the ransom message is in choppy English and Polish (Odzyskaj pliki *.cezor), hinting at CEE affiliate involvement.
  • Network spread limitation: Encrypted NAS/UNC shares are not reinfected from the active Windows node; this allows you to safely mount shadow copies from another workstation.
  • Post-breach data leak? To date, cezor intrusions have not been coupled with exfiltration (confirmed by shred-case reviews from Coveware & Unit42). Files remain only encrypted, not leaked on dark web.

Summary Checklist (Quick Print)
☑️ Patch MS17-010 & BlueKeep, block TCP-3389, enforce MFA.
☑️ Immutable off-line backups + test restore.
☑️ Endpoint EDR + Autoruns for manual persistence cleanup.
☑️ Expect NO free decryptor; prepare offline restore plan rather than payment.