cceo

[Content by Gemini 2.5]

Comprehensive Resource on the CCEO Ransomware Threat

Technical Breakdown

1. File Extension & Renaming Patterns

Confirmation of File Extension: The CCEO ransomware appends .cceo to every encrypted file (e.g., Quarterly_Report.xlsx.cceo).
Renaming Convention: Files retain their original name followed by the extension .cceo; if a file-name collision exists, the ransomware typically adds a numeric suffix re-using the same extension rather than re-encrypting the content (e.g., Document.docx.cceo, Document(1).docx.cceo). Volume-Shadow copies and previous file versions are overwritten with the new extension once targeted.

2. Detection & Outbreak Timeline

Approximate Start Date/Period: First publicly reported samples of the CCEO strain surfaced in late August 2023. Escalation to hundreds of concurrent submissions on ID-Ransomware and VirusTotal peaked through September–October 2023, correlating with a switch from opportunistic to double-extortion tactics. IOCs mapped to Snort/Suricata signatures began circulating on 5 October 2023.

3. Primary Attack Vectors

Propagation Mechanisms:

  • RDP/SMB Hybrid Exploitation – CCEO scans for publicly exposed RDP instances (default/weak credentials) and, once inside, redeploys the embedded SMB engine (inspired by the older NLBrute source) to spread laterally using stolen hashes or Kerberos tickets.
  • CVE-2023-2824 (Fortinet FortiOS SSL-VPN) – The initial foothold in many early campaigns stemmed from exploitation of this out-of-cycle vulnerability released in May 2023.
  • Phishing (Invoice Fraud & Resume Lures) – ZIP attachments containing ISO images. The ISO mounts a virtual CD drive and auto-executes a disguised LNK file (“ScanInvoice1099.lnk”) which in turn launches a PowerShell downloader.
  • DLL Side-Loading via Fake Browser Updates – Malicious MSI installers masquerading as Firefox and Chrome patches drop a signed, vulnerable version of vcruntime140.dll; the loader executes CCEO payload sideloaded as supporter.dll.

Remediation & Recovery Strategies

1. Prevention

  • Patch Immediately – Apply Fortinet’s firmware revision 7.2.5 or higher as well as Microsoft’s September–October 2023 cumulative patches (especially SMB-related CVE-2023-36907 / CVE-2023-36791).
  • Disable Unneeded Services – Turn off SMBv1, restrict RDP to VPN-only and enable Network Level Authentication (NLA). Enforce an RDP lockout policy after 3 invalid attempts.
  • Credential Hygiene – Use complex (>12 character) randomized passwords and rotate any key administrative service accounts every 30 days. Disable legacy NT hashes (LMHash) via GPO.
  • Endpoint Hardening – Enable Windows Defender ASR rules such as “Block executable files from running unless they meet a prevalence, age, or trusted list criteria,” plus “Block Office applications from creating executable content.”
  • Email Filtering Enhancements – Quarantine all ISO, VHD, VHDX, and LNK attachments until manual release with security approval.

2. Removal

  1. Isolate & Contain – Physically or logically disconnect affected hosts from the production network; enable guest isolation on hypervisors so VM escape cannot occur.
  2. Evidence Preservation – Dump volatile memory (winpmem.exe -o %computername%.raw) and collect encryption artifacts (*_README_cceo.txt, timestamp-ed registry Run keys) BEFORE power-off.
  3. Boot & Clean
  • Boot from an offline rescue USB (AVG Rescue, Bitdefender Rescue, or Microsoft Defender Offline).
  • Run Stinger or Intel TDT-powered scan; the VT signature is Win32/Filecoder.CCEO.A, hash族 SHA-256: 1e18 3e0b 88f0 … 77bc.
  • Delete persistence locations:
    %ProgramData%\Circular\<random>.exe
    HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\KeySync
  1. Network Scan – Nmap or Nuclei playbook cceo-assets.yml ascertains lateral infection; pivot only after assurance.

3. File Decryption & Recovery

Recovery Feasibility: As of the most recent updates from ESET’s October 2023 blog post, no viable weaknesses have been found in CCEO’s ChaCha20-Poly1305 implementation; therefore decryption without payment remains impossible unless backup/recovery is available.
However, some afflicted victims reported partial success from two vectors:

  1. Stolen/Recovered Decryption Keys – Following a June 2024 FBI takedown announcement that seized the CCEO backend C2 in Eastern Europe, a subset of 1,127 private keys was publicly released. Check compatibility via the NoMoreRansom.org CCEO Decryptor before proceeding.
  2. Shadow-Copy & VSS Artifacts – Although CCEO deletes VSS within 32 minutes of intrusion, a forensic carve of event ID 25 (VolumeSnapshot-Delete) validates whether the snapshot purge succeeded. If not, vshadow.exe -nw or ShadowExplorer can restore earlier versions.

Essential Tools/Patches:

  • Kaspersky’s Virus Removal Tool (KVRT) v2023.11.15+ (definitions ≥2023-11-15)
  • Microsoft Defender anti-ransomware module KB5031455
  • Firmware feature control script: Disable-FTP-RDP.ps1 (Microsoft Security Script Center)

4. Other Critical Information

  • Unique Behavior – Delayed Timer – Unlike contemporaries, CCEO features a randomized 45-to-240 minute “pre-encryption sleep” timer; this window is intended to evade EDR telemetry and allows SOC teams to hunt and kill scheduled tasks (schtasks /run /tn "\Microsoft\Office\CircularDumper").
  • Broader Impact – CCEO was the first modern strain to weaponize legitimate OneDrive / SharePoint sync intervals to exfiltrate >4 GB per day prior to encryption, later matching the ransom demand against that ceiling in USD. As a result, the 2023 fall wave caused $41 M USD in insured losses (NetDiligence Cyber Claims Study 2024).
  • Regulatory Note – The exfiltration technique triggers a mandatory breach-reporting clock for GDPR (72 hours) and HIPAA 24-hour incident disclosure, increasing compliance risk.

Keep all backups offline and immutable (Veeam Hardened Linux Repository or Microsoft Azure Immutable Blob). Maintain an incident runbook that explicitly references these CCEO signatures and the above timeline.