CVE-2026-53581: Opnsense Core

Critical severity, CVSS 9.0. EPSS: 0.5% chance of exploitation in the next 30 days.

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.

Affected products

• Opnsense Core: before 26.1.9 (fixed in 26.1.9); before 26.4_20 (fixed in 26.4_20)

Published 2026-09-08. Last modified 2026-09-25.