cesar

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Cesar locks files by appending “.cesar” (or “.cesar” suffix followed by the master cybercriminal’s e-mail address, e.g., “.cesar[[email protected]]”).
  • Renaming Convention: The malware keeps the original file name and positions the extension at the end
    Example:
    Q1_2024_Report.xlsx → Q1_2024_Report.xlsx.cesar

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The first confirmed samples were observed mid-January 2018, shortly after a rash of DOTA-related C# ransomware. A large wave of Cesar infections peaked May-June 2018, coinciding with an increase in brute-force and exploit-kit deployment. Sporadic bursts continue to surface into 2024 via cracked-software and compromised MSSQL servers.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    • Remote Desktop (RDP) brute-forcing – Cesar operators aggressively scan for open 3389/TCP, trying common or recycled credentials.
    • EternalBlue / DoublePulsar – Early samples shipped with an embedded NSA exploit pack to propagate laterally over SMBv1 (CVE-2017-0144 is still leveraged on un-patched 2008/2012 machines).
    • Malicious e-mail attachments – Office docs with malicious VBA macros that download the payload from a Pastebin or Discord CDN link.
    • Cracked software and game “keygens” – Repack installers drop the main DLL in %TEMP% which is executed via regsvr32.exe or rundll32.exe.
    • Weak SQL Server credentials – Borrows from GlobeImposter tactic: brute-forces sa logins and uses xp_cmdshell to push the ransomware binary.

Remediation & Recovery Strategies:

1. Prevention

  • Apply MS17-010 and enable “SMBv1 off” across Windows fleet immediately.
  • Restrict RDP to VPN only: force Network Level Authentication (NLA) and disable NTLM if possible; insist on complex passwords + account lockout.
  • Deploy an EDR/AV solution with ETERNALBLUE, Mimikatz-lateral, and cmd.exe obfuscation detections enabled.
  • Filter mail for .doc/.xlsm macros and auto-run from %TEMP% and %APPDATA%.
  • Maintain offline & off-site backups with immutable/credential-less access tested quarterly.
  • Monitor SQL/MSSQL for repeated failed logins; segregate fully from user-backup network.

2. Removal

  1. Isolate the infected host (pull the NIC cable, disable Wi-Fi/Bluetooth).
  2. Boot into Safe Mode w/ Networking or your preferred incident-response PE (Hiren, Kaspersky Rescue).
  3. Kill & Remove persistence:
    • Delete the dropped file (%AppData%\svchsot.exe, %ALLUSERSPROFILE%\System32\(random)\random.dll).
    • Scrub accompanying scheduled task: schtasks /delete /tn "WindowsUpdateCheck" /f
    • Inspect HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce and analogous Run keys for randomized entry.
  4. Run a trusted remediation sweep (ESET Online Scanner, Malwarebytes, MSERT, etc.) to confirm complete eradication before reconnecting.

3. File Decryption & Recovery

  • Recovery Feasibility: **NO public *FREE* decryptor exists for .cesar.**
    – The ransomware uses a hybrid RSA-2048 + AES-128 cipher; private master key is out of reach unless law-enforcement seizes one of the operator’s servers (has occurred in just two reported cases, and victims still had to pair the key generation to their own victim ID).
    – Option 1 – Paying Ransom: Not recommended (no guarantee + legal/regulatory risk).
    – Option 2 – Data Recovery via Shadow Copies: Cesar deletes all Volume Shadow Service (VSS) entries with the command vssadmin delete shadows /all /Quiet. However, if an endpoint was powered off or VSS was already disabled, forensic tools like ShadowExplorer or power-on snapshots (Hyper-V, VMware, Veeam) occasionally recover intact copies.
    – Option 3 – Offline/Offline-NAS Backups: Redcell-level restores remain the single reliable mechanism.

4. Other Critical Information

  • Ransom Note(s): Two plaintext notes appear on every volume:
    HOW TO RECOVER ENCRYPTED FILES.TXT (or .hta)
    and README_DECRYPT.HTML on the desktop. Both point to onion site (hbmn5lw4zlfxpwwz[.]onion) and e-mails (↑ displayed inside the note: e.g., [email protected] and [email protected]).
  • Unique traits:
    – Shares >85 % code overlap with Dharma/Crysis, indicating the same affiliate framework.
    – Offers a single-file test decryption, but will demand separate, higher amount if you try large directories.
  • Broader Impact: Because Cesar is a ‘commodity’ strain sold on underground markets, infrastructure hit ranges from dental clinics to global manufacturing. High-profile outages occur where legacy Windows 7/2008 systems overlap with exposed RDP; healthcare and educational institutions remain top targets.