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CVE-2026-65639 – Root OS Command Injection – ConfigServer Security & Firewall (CSF) 2.15 to < 16.30

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Summary

CVE-2026-65639 is an OS command injection vulnerability in the advanced-rule parser of ConfigServer Security & Firewall (CSF), a widely deployed Linux firewall and intrusion-detection tool commonly used on cPanel/WHM servers. A remote attacker who controls a configured allow/deny feed can inject and execute arbitrary commands as root due to insufficient validation of feed-supplied rule data. The flaw carries a CVSS score of 9.5 (Critical).

Technical details

  • Root cause: CSF’s advanced-rule parser processes rule data pulled from configured allow/deny feeds without sufficient validation, allowing embedded OS commands to be executed.
  • Trigger conditions: The target server must be configured to consume an allow/deny feed that is (or becomes) attacker-controlled or attacker-influenced; the malicious feed data is then parsed by CSF’s advanced-rule logic.
  • Attack vector: Network — no direct interaction with the target server is required beyond the server fetching/processing the attacker-influenced feed content.
  • Impact: Successful exploitation results in arbitrary command execution with root privileges, giving full compromise of confidentiality, integrity, and availability of the affected host.

Affected software

  • WebPros ConfigServer Security & Firewall: versions 2.15 up to (but not including) 16.30
  • ConfigServer (original/legacy) ConfigServer Security & Firewall: versions 2.15 and later (no fixed version available from the original maintainer)

Severity

CVSS v4.0 Base Score: 9.5 (Critical)
Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

Mitigation and recommended actions

  • Immediate: Upgrade WebPros-maintained CSF installations to version 16.30 or later, where the vulnerability is remediated.
  • If no patch is available: Servers running the original, no-longer-maintained ConfigServer releases (which the original developer stopped supporting after August 31, 2025) have no vendor-supplied fix. Administrators of these installations should disable or remove any configured allow/deny feed integrations, restrict CSF to feeds from fully trusted, verified sources only, and evaluate migrating to the actively maintained WebPros/cPanel fork of CSF.

References

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