OPNsense prior 26.1.9/26.4_20 NTP Configuration /opnsense/core GPS/PPS serial port path traversal

Summaryinfo

A vulnerability was found in OPNsense. It has been declared as very critical. The affected element is an unknown function of the file /opnsense/core of the component NTP Configuration Module. Such manipulation of the argument GPS/PPS serial port leads to path traversal. This vulnerability is listed as CVE-2026-53581. The attack may be performed from remote. There is no available exploit. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability was found in OPNsense. It has been rated as very critical. Affected by this issue is some unknown processing of the file /opnsense/core of the component NTP Configuration Module. The manipulation of the argument GPS/PPS serial port with an unknown input leads to a path traversal vulnerability. Using CWE to declare the problem leads to CWE-22. The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. Impacted is confidentiality, integrity, and availability. CVE summarizes:

OPNsense is a FreeBSD based firewall and routing platform. Prior to version 26.1.9 of opnsense/core and version 26.4_20 of BE/opnsense/core, a path traversal vulnerability in the NTP configuration module allows an attacker to overwrite arbitrary files on the system as the root user. By manipulating the GPS or PPS serial port parameter, an attacker with access to the NTP configuration can escape the intended directory and force the system to write user-controlled data to any file on the filesystem. Version 26.1.9 of opnsense/core and version 26.4_20 of BE/opnsense/core patch the issue.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-53581 since 06/09/2026. The exploitation is known to be easy. The attack may be launched remotely. Additional levels of successful authentication are necessary for exploitation. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 09/09/2026). The MITRE ATT&CK project declares the attack technique as T1006.

Upgrading to version 26.1.9 or 26.4_20 eliminates this vulnerability.

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• OPNsense

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