CVE-2026-58391 OPNsense: Stored XSS in Firewall Rules/NAT pages via a HTML-attribute breakout
Stored XSS in OPNsense firewall rules allows attackers to execute scripts in admin sessions, potentially leading to account takeover.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-58391?
CVE-2026-58391 is a medium-severity cross-site scripting vulnerability in opnsense core, published on 15 Oct 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official description
OPNsense is a FreeBSD based firewall and routing platform. Prior to version 26.1.11, Firewall Rules and NAT views place stored category names and alias descriptions into HTML title attributes in filter_rule.volt and nat_rule.volt without quote-safe encoding. The response layer uses ENT_NOQUOTES, so a double quote survives and closes the attribute, allowing an event-handler attribute to be added to the existing span. A user with Firewall Categories or Firewall Alias Edit privileges can store a category name or alias description; the category must be assigned to a filter or NAT rule, or the alias must be referenced by a rule source or destination, and the rule must be saved so the affected tooltip is rendered. Script then executes in the session of an administrator or other user who opens the affected Rules or NAT page. The script can access CSRF material and perform authenticated actions as the victim. This issue is fixed in version 26.1.11.
Which versions are affected by CVE-2026-58391?
How do I fix CVE-2026-58391?
No fix has been published for CVE-2026-58391 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-2026-58391 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-58391 exists.
Sources
Also known as GHSA-2xrm-p255-p43h.