CVE-2019-25375 OPNsense 19.1 Reflected XSS via monit interface

Medium 5.1 Published 15 Feb 2026 Updated 24 May 2026

Unauthenticated attackers can inject malicious scripts via the monit interface mailserver parameter, executing code in victim browsers.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: A user has to click or open something
Fix: None listed

What is CVE-2019-25375?

CVE-2019-25375 is a medium-severity cross-site scripting vulnerability in OPNsense, published on 15 Feb 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

Official description

OPNsense 19.1 contains a reflected cross-site scripting vulnerability that allows unauthenticated attackers to inject malicious scripts by submitting crafted input to the mailserver parameter. Attackers can send POST requests to the monit interface with JavaScript payloads in the mailserver parameter to execute arbitrary code in users' browsers.

Weakness: CWE-79

Which versions are affected by CVE-2019-25375?

It affects 1 product.

Products include Opnsense Opnsense.

How do I fix CVE-2019-25375?

No fix has been published for CVE-2019-25375 yet. Limit exposure of the affected software until one is available.

Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.

Is CVE-2019-25375 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2019-25375 exists.

Sources

Also known as GHSA-6333-cc9f-9589.