CVE-2026-67599: ClearOS 7.9 RCE Vulnerability

CVE-2026-67599 Overview

CVE-2026-67599 is an operating system command injection vulnerability in the Log Viewer component of ClearOS 7.9. The flaw resides in File.php, where the filter parameter is interpolated directly into a shell command without sanitization. Authenticated attackers can submit command substitution payloads through this parameter to execute arbitrary commands as the webconfig user. Because the webconfig account is granted extensive NOPASSWD sudo privileges by default, attackers can immediately escalate to root. The issue is classified under CWE-78: Improper Neutralization of Special Elements used in an OS Command.

Critical Impact
Authenticated attackers can inject shell commands via the Log Viewer filter parameter and pivot to root through default NOPASSWD sudo rights on the webconfig user.

Affected Products

ClearOS 7.9
ClearOS Log Viewer component (File.php)
Deployments running with the default webconfig sudo configuration

Discovery Timeline

2026-08-03 - CVE-2026-67599 published to NVD
2026-08-04 - Last updated in NVD database

Technical Details for CVE-2026-67599

Vulnerability Analysis

The Log Viewer feature in ClearOS 7.9 accepts a user-controlled filter parameter and passes it into a shell command constructed in File.php. The value is interpolated into the command string without escaping or allow-list validation. This allows an authenticated user of the ClearOS web administration interface to break out of the intended argument context.

Submitting a payload containing shell metacharacters such as backticks or $() triggers command substitution inside the shell invocation. The injected commands run under the webconfig service account that hosts the ClearOS administration UI. The EPSS probability for this CVE is approximately 1.91%.

The severity is amplified by ClearOS defaults. The webconfig user has broad NOPASSWD sudo entries, so any command executed through the injection can be re-issued with sudo to run as root. Attackers gain full control of the appliance, including access to firewall rules, VPN configuration, and stored credentials.

Root Cause

The root cause is missing input neutralization on the filter parameter before it is embedded in a shell command line [CWE-78]. Safer alternatives such as parameterized process invocation, strict allow-list validation, or shell metacharacter escaping are not applied in File.php.

Attack Vector

Exploitation requires network access to the ClearOS webconfig interface and valid authenticated credentials with permission to view logs. The attacker issues an HTTP request to the Log Viewer endpoint with a crafted filter value containing a command substitution payload. The web application concatenates the payload into the shell command, the shell executes the substitution, and the injected command runs as webconfig. A follow-on sudo call promotes execution to root.

See the VulnCheck Advisory: ClearOS Command Injection for technical details.

Detection Methods for CVE-2026-67599

Indicators of Compromise

HTTP requests to ClearOS Log Viewer endpoints containing shell metacharacters such as `, $(, ;, |, or && in the filter parameter.
Child processes spawned by the ClearOS webconfig PHP process that are inconsistent with normal log-parsing binaries.
Unexpected sudo invocations originating from the webconfig user on the appliance.
New or modified files under /root, /etc, or /var/webconfig that correlate with Log Viewer access.

Detection Strategies

Inspect webconfig HTTP access logs for filter parameter values containing shell metacharacters and URL-encoded equivalents (%60, %24%28).
Correlate Log Viewer requests with process execution telemetry showing shell or interpreter processes as descendants of the PHP handler.
Alert on any sudo execution by webconfig outside of documented administrative workflows.

Monitoring Recommendations

Forward ClearOS webconfig access logs, auth.log, and sudo logs to a central SIEM for correlation.
Baseline expected child processes of the webconfig PHP process and alert on deviations.
Monitor outbound network connections from the ClearOS host for reverse shells originating after Log Viewer requests.

How to Mitigate CVE-2026-67599

Immediate Actions Required

Restrict network access to the ClearOS webconfig interface to trusted management networks only.
Rotate all administrative credentials used to authenticate to the ClearOS web interface.
Audit the webconfig sudoers configuration and remove unnecessary NOPASSWD entries where feasible.
Review recent Log Viewer access logs for injection attempts and evidence of prior exploitation.

Patch Information

No vendor patch is referenced in the available advisory data for CVE-2026-67599. Refer to the ClearOS Official Website and the VulnCheck Advisory: ClearOS Command Injection for the latest vendor guidance and remediation status. Given that ClearOS 7.x has reached end-of-life status for many components, plan migration to a supported platform.

Workarounds

Block or firewall the webconfig HTTPS management port from untrusted networks and require VPN or bastion access.
Disable the Log Viewer module in ClearOS webconfig if it is not required for operations.
Introduce a reverse proxy in front of webconfig that rejects requests where the filter parameter contains shell metacharacters.
Tighten /etc/sudoers.d/ entries for the webconfig user to reduce blast radius if injection succeeds.

bash

# Example reverse-proxy filter rule (nginx) rejecting shell metacharacters
# in the Log Viewer filter parameter
if ($arg_filter ~* "[`;|&$()<>]|%60|%24%28") {
    return 403;
}