Vulnerability in Discourse

CVE-2026-91132

Discourse is an open-source discussion platform. Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0, sites using wildcard patterns in the allowed_iframes setting could accept a crafted iframe URL whose allowlisted suffix appeared after a URL authority separator. The wildcard origin check matched the allowed domain text, while browser URL parsing selected a different attacker-controlled origin. A user with posting privileges could exploit the flaw through a post or a Onebox oEmbed response and cause an attacker-controlled iframe to be rendered independently of the allowlisted domain. Successful exploitation requires a site-configured wildcard iframe pattern and the ability to create a post or trigger an oEmbed request for an attacker-controlled URL. This issue is fixed in versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0.

Published · last modified .

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N.

EPSS exploit prediction

EPSS: 0.001 (3.0th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 3rd percentile — 3.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-91132: held from 0.001 to 0.001.

EPSS over last 30 days · oldest: 0.001 · newest: 0.001 · change: 0.000

Affected products

  • Discourse — versions < 2026.8.0, >= 2026.1.0-latest, < 2026.1.8, >= 2026.6.0-latest, < 2026.6.3

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-91132?
CVE-2026-91132 is a medium-severity vulnerability in Discourse, classified under Origin Validation Error. CVSS score: 4.3/10. Published 2026-09-24.
How severe is CVE-2026-91132?
Medium severity. CVSS v3 base score is 4.3 out of 10.