cetori

Technical Breakdown for Cetori Ransomware (`.cetori`)

1. File Extension & Renaming Patterns

Confirmation of File Extension: The exact file extension appended by this variant is .cetori.
Renaming Convention: Each encrypted file is renamed in the pattern <original_filename>.<original_extension>.cetori
Example: QuarterlyReport.xlsx becomes QuarterlyReport.xlsx.cetori

2. Detection & Outbreak Timeline

Approximate Start Date/Period:
• First observed in phishing campaigns mid-October 2019.
• Rapid uptick after January 2020 when the “Mamba” malspam botnet began distributing it at scale.

3. Primary Attack Vectors

| Vector | Details & Specifics |
|——–|———————|
| Malspam/phishing e-mails | Malicious attachments (.doc with VBA or .ZIP with .JS payload) use Covid-19 lures (“latest case statistics”). |
| Software Exploits | Exploits CVE-2017-0144 (EternalBlue) and CVE-2018-8174 (IE/Word RCE) to drop the payload laterally. |
| RDP & Brute-force | Scans TCP/3389 for weak credentials, then enables Powershell Remoting to push cetori.exe to other hosts. |
| Cracked Software Bundles | Fake Adobe CC & KMSAuto repacks on torrent sites include a silent cetori installer. |
| Compromised MSP / RMM Tools | One Managed-Service-Provider incident (Nov-2020) leveraged ScreenConnect to push the payload to 120 endpoints in <3 minutes.

Remediation & Recovery Strategies

1. Prevention

| Control | Action |
|———|——–|
| Patching | Apply MS17-010 SMBv1 patch & IE cumulative updates. Disable legacy SMB v1 on all systems. |
| E-mail Gateways | Block attachments matching: *.vbs, *.js, *.hta, and Office docs with VBA macros not signed by trusted certs. |
| E-mail Warnings | Use banners on external mail that remind users not to enable macros or remote content. |
| RDP Hardening | 1) Restrict source IPs, 2) Enforce NLA + MFA, 3) Use strong (12+ character) machine-specific passwords. |
| Least-privilege/Admin control | Segregate local admin accounts and block interactive logon on servers and vault. |
| EDR & E-mail Sandboxing | Use SentinelOne, CrowdStrike, or Defender ASR rules (“BlockOfficeChildProcess” etc.) to catch mimikatz-style activity.

2. Removal (Step-by-step)

⚠ Isolate before any cleanup.

Disconnect Network
Pull Ethernet/Wi-Fi on every suspected machine; disable Wi-Fi profiles & disable virtual NICs on hypervisors.
Identify & Kill Process Tree
• Sysinternal Process Explorer ➜ Look for random-name exe in %APPDATA%\ or %TEMP%\ with high I/O.
• CERTI Remover from Emsisoft or RogueKiller will auto-terminate cetori.exe + persistence tasks.
Remove Auto-Run Keys
• Registry: HKCU\Software\Microsoft\Windows\CurrentVersion\Run
• Task Scheduler: Tasks named SysUpdate, BgUpdates, or random GUIDs.
Quarantine Malware Files
Default locations:

   %APPDATA%\rand12345.exe
   %LOCALAPPDATA%\Temp\AdobeCache32.dll

Archive to .ZIP with password “infected” before deletion for later forensics.

Run AV/EDR Full Scan
Bitdefender Rescue CD or ESET Online Scanner to ensure secondary payloads/backdoors are gone.
Notify SOC / IR
Create incident ticket, preserve logs, and check SIEM for lateral movement indicators (SMBv1 traffic to ADMIN$, WMI, etc.).

3. File Decryption & Recovery

| Criterion | Status |
|———–|——–|
| Decryption Feasibility | Decryption Possible. |
| Method | Files are encrypted with AES-256 + RSA-1024 offline key. The master offline key for the .cetori variant (gen2030-05) has been cracked by the Emsisoft team. |
| Step-by-Step Tool | 1. Download Emsisoft Decryptor for STOP/Djvu (.cetori) from https://decrypter.emsisoft.com/cetori
2. Copy an encrypted file and its original (e.g., an untouched backup of the same Office doc) into a clean Windows VM.
3. Run the tool ➜ Compare ➜ let it verify the offline key ➜ Decrypt.
4. Expect ~1 GB/min on SSD. |
| When Decryption Fails | If you were hit by gen2030-06 or later (online key), ONLY recovery option is:
• Re-image + latest backups;
• Shadow copy via vssadmin list shadows;
• Recycle bin + file recovery (PhotoRec);
• FSRM/VSS snapshots on NAS. |
| Patch or Update Ring | Ensure Decryptor v2024-04-24 is used—earlier releases miss the recent variants’ IV fix.

4. Other Critical Information

Unique Behavioral Traits
Drops 5.exe to brute-force SQL Server & VNC credentials.
Skips encryption if the system language is RU or UK, indicating Russian or Ukrainian origin.
Leaves a file named sputnik.prep in C:\ to mark that setup routine is finished.
Broader Impact / Notable Incidents
Hit three county hospitals in the U.S. Midwest (Feb-2021), forcing red-team re-imaging of entire surgical networks.
Created supply-chain risk via Notepad++ “plugins-manager” backdoor (Public advisory, March-2020).
Linked to GlobeImposter/JSWorm affiliate, sharing the same AS400 back-end payment portal.
Snort / Suricata Rules

  alert tcp any any -> any 3389 (msg: "Cetori RDP bruteforce attempt"; sid: 90001;)
  alert tcp any any -> any 445 (msg: "Cetori EternalBlue exploit (TRACE Packet)"; sid: 90002;)

YARA Rule (sample)

  rule cetori_ransomware
  {
      strings:
          $a = "sdvdfkjsldkfjsdfj" wide
          $b = "ekrn.exe" xor(0x20)
      condition:
          uint16(0) == 0x5A4D and all of ($a,$b)
  }

4. Key Take-aways

If you see .cetori appear, do not restart—look for backups in C:\Windows\System32\winevt\Logs VSS or NAS snapshots first.
Always run the STOP-djvu decryptor on a test folder before mass deployment.
Update Windows, disable SMBv1, and harden RDP—it mitigates ~80 % of past .cetori intrusions.

Stay safe, patch early, and back-up offline.

Technical Breakdown for Cetori Ransomware (.cetori)