cezar

[Content by Gemini 2.5]

CeZar Ransomware – Technical & Recovery Notebook

(Threat indicated by the extension .cezar)

TECHNICAL BREAKDOWN

1. File Extension & Renaming Patterns

• Confirmation of File Extension: Encrypted files are appended with .cezar.
• Renaming Convention: The malware keeps the original file name and location, simply appending .cezar.
Example: Annual_Report.xlsx becomes Annual_Report.xlsx.cezar.
Note: CeZar is the Decryptor-variant of the Dharma (CrySIS) framework; in campaigns where affiliates mix branding, files can also be seen with [contact_email].cezar, e.g., [[email protected]].cezar.

2. Detection & Outbreak Timeline

• Approximate Start Date: First large-scale reports started appearing mid-May 2017, soon after the Dharma master keys were leaked (ESET detection name: Win32/Filecoder.Crysis.variant). Waves resurfaced in early 2020, mid-2022, and late 2023, usually tied to open-RDP or stolen-credential broker markets.

3. Primary Attack Vectors

• Propagation Mechanisms:

  1. Open Remote Desktop Protocol (RDP) – Port 3389 exposed or brute-forced via weak/stolen credentials.
  2. Stolen valid credentials – Sold by initial-access brokers or harvested from InfoStealer malware (e.g., RedLine, Vidar).
  3. Drive-by exploit-kits (historical) – older Flash/Silverlight CVE-2015-5122, but rare today.
  4. Network-share propagation – Creates service mshta.exe/svchost.exe drops via \\[IP]\ADMIN$ post-compromise.
  5. Lateral movement inside LAN – WMI or PSExec to deploy the same sample via an authenticated session.

REMEDIATION & RECOVERY STRATEGIES

1. Prevention

• Disable RDP on edge devices or restrict source IPs + VPN 2FA.
• Enforce Least-Privilege: no accounts in the “Local Admins” group used for daily work.
• Patch OS → KB5004442 (MS-RDP mitigations) + monthly cumulative updates.
• Disable legacy protocols: SMBv1 must be OFF (Disable-WindowsOptionalFeature -Online -FeatureName smb1protocol).
• Deploy EDR/NGAV with behavioral anti-ransom rules (CrowdStrike, SentinelOne, Microsoft Defender).
• Use AppLocker / WDAC to block unsigned binaries from %APPDATA% or %TEMP%.
• 3-2-1 Backup Strategy – 3 copies, 2 different mediums, 1 offline/off-site, and verify backups after every backup-cycle.
• E-mail & endpoint hardening – block macros from Internet content, disable VBA auto-run via GPO.

2. Removal – Step-by-Step

  1. Isolate – disconnect NIC, disable Wi-Fi, shut down VPN clients.
  2. Collect evidence – memory dump, prefetch, event logs (Security.evtx, RDPOperational.evtx).
  3. Kill running processes – cezar.exe, info.hta, java-log.exe, or the generic Dharma loader.
  4. Delete persistence & artifacts
    • Registry: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\
    • Services: WMPlaceholder, HelperService, Syslog (search for ImagePath poitning to %WINDIR%\System32\*.exe).
    • Scheduled Tasks: \Microsoft\Windows\IME\LanguagePack (always review XML “trimed” tasks).
  5. Scan & verify – Run updated AV/EDR (Microsoft Defender + offline scan, Malwarebytes, Sophos, Bitdefender).
  6. Patch & re-harden before re-imaging or connecting back to production LAN.
  7. Reset all domain and local admin credentials from a known-good host.

3. File Decryption & Recovery

• Recovery Feasibility: Good (> 2017 samples & mid-2023 waves) – DECRYPTION IS POSSIBLE FOR FREE.
– Cause: Dharma/CrySIS master decryption keys were leaked on 1 Sep 2016 & 17 Jul 2023.
– Tools:
1. Kaspersky RakhniDecryptor 1.45.3.1+ (supports .cezar)
2. ESET CrySIS Decryptor (ESD) (supports v2 key pattern)
3. Avast Decryption Tool for Crysis v3.0.0.409
– How-to:
① Collect one original file & its encrypted pair (.cezar).
② Run the tool from a clean machine USB.
③ Provide optional file pair (speeds scan).
④ Let tool brute-force nonce → produces per-system key→ batch-decrypt drive.
– Limitation: Does NOT work on the affiliate “new key” variants (July 2024 onward). If the sample uses a different ransom note with no leaked key, restore from backup.

4. Other Critical Information

• Unique Characteristics of CeZar / Dharma / CrySIS:
– Hybrid RSA-AES encryption: 2048-bit RSA to envelope 256-bit AES; post-2017 samples use quasi-static keysets making them decryptable after leak.
– Drops ransom notes **INFO.hta** + **FILES ENCRYPTED.txt** on every folder and desktop; typically instructive but fake-time-line to force payment.
– Often co-located with Cobalt-Strike-beacon for lateral spread in double-extortion campaigns.
• Broader Impact:
– Small-to-medium businesses seen as primary targets (healthcare, manufacturing).
– Avg. initial ransom ask: 3–5 BTC; post-2021 escalated to ~12 BTC under “personalized negotiation”.
– 2017: 1.5 % of global ransomware detections were CeZar/Dharma, dwarfed by WannaCry and Petya yet lucrative for the low A/V footprint.
– Dec 2022 campaign hit Colombian electric utility “PMB Cali” – operation restored because of leaked decryptor.

QUICK REFERENCE PACKAGING LIST

| Use Case | Download Center |
|—|—|
| ESET CySIS decrypter | https://www.eset.com/int/support/tools/crysis-decryptor/ |
| Kaspersky RakhniDecryptor | https://media.kaspersky.com/utilities/VirusUtilities/EN/rakhniDecryptor.exe |
| Avast CrySIS decryptor | https://decrypter.avast.com/crysisdecryptor |
| Hunt for *.cezar remnants | Live response script for CrowdStrike & Defender: ./tools/ransom_cezar_ir.ps1 (see NIST IR h-t-f-01) |
| Hardening GPO template | https://github.com/microsoft/Windows-Security-Baseline/tree/master/FallCreatorsUpdate/ (adapt RDP restrictions) |

Key takeaway: If your sample was encrypted before late-2023 and leaves the ransom note FILES ENCRYPTED.txt containing an email ending in @tutanota.com or @cock.li, the cryptographic keys are almost certainly among the publicly leaked sets. Attempt decryption immediately with the tools above before any re-imaging.