CVE-2026-583915.4MediumCWE-83

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

opnsense · core

Affected: opnsense core · Exploitation: unlikely (under 1%)

Not in CyberSIXT coverage yet: no article names this CVE. This page shows the public record.

0.3%probability of exploitation in the next 30 days

20th percentile

050100

Higher than 20% of scored CVEs

5.4MediumCVSS 3.1

LowMediumHighCrit.

DescriptionCVE.org

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.

Affected products1

From the CVE record. A product or version that is not listed is unknown, not unaffected.

opnsense · core< 26.1.11

On the Atlas

Every published CVE is on the CyberSIXT Atlas, grouped by weakness, vendor and month.

Open the Atlas

Exploitation: Unlikely (under 1%). EPSS under 1%, or no score yet.
CISA KEV: Not listed
Public check: No public nuclei template
Weakness: Improper Neutralization of Script in Attributes in a Web Page · Cross-site Scripting
Vendor: opnsense
Published: October 2026
Band: Unlikely (under 1%), October 2026

CoverageNo articles yet

No CyberSIXT article names CVE-2026-58391 yet, so there is no coverage timeline, action brief or change log for it. Everything on this page comes from the public CVE record, CISA KEV, EPSS and the nuclei template index. Search the archive or see the CVEs in the news.