CVE-2026-58391: OPNsense stored cross-site scripting in firewall rule and NAT tooltips

CVE-2026-58391 · Severity: medium · CVSS 5.4 · Published 2026-10-15

OPNsense is a FreeBSD-based firewall appliance that manages network traffic and routing. Prior to version 26.1.11, users with firewall configuration privileges could inject malicious code into category names or alias descriptions that execute in the browser of administrators viewing the firewall rules or NAT configuration pages. An attacker with limited privileges can steal session credentials and perform unauthorized firewall configuration changes on behalf of targeted administrators.

Technologies: OPNsense. Vendors: OPNsense.

Quick answers

Is CVE-2026-58391 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-58391 being exploited in the wild.
How severe is CVE-2026-58391?
Medium severity, with a CVSS score of 5.4, published 15 October 2026.
Which products and versions are affected?
OPNsense prior to 26.1.11.
Is there a fix for CVE-2026-58391?
Yes: fixed in 26.1.11. Until then: Restrict Firewall Categories and Firewall Alias Edit privileges to trusted administrators only, and limit access to the firewall rule and NAT configuration pages. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-58391 attacked?
It is attacked over the network.
Am I affected by CVE-2026-58391?
Check whether you run OPNsense at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • Fixed in: 26.1.11

Restrict Firewall Categories and Firewall Alias Edit privileges to trusted administrators only, and limit access to the firewall rule and NAT configuration pages.

Technical details

The vulnerability is a stored cross-site scripting (XSS) flaw in the filter_rule.volt and nat_rule.volt view templates where user-controlled category names and alias descriptions are embedded into HTML title attributes without proper encoding. Although the response layer uses ENT_NOQUOTES, double quotes remain unescaped, allowing an attacker to close the title attribute and inject event-handler attributes on the tooltip span element. The attack requires a user with Firewall Categories or Firewall Alias Edit privileges to store the payload and have it rendered via a firewall or NAT rule, after which the injected script executes in the session context of any administrator or other user viewing the affected page.

Affected products

  • OPNsense OPNsense prior to 26.1.11

Timeline

  • 2026-10-15: disclosed
  • 2026-10-15: patched

References

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