XSS in Discourse
CVE-2026-91122
Discourse is an open-source discussion platform. Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0, the video placeholder component allowed crafted HTML to cause an attribute breakout and inject an attacker-controlled event handler. An authenticated user with default trust-level posting privileges could store the crafted placeholder in a post. When another user opened the post and clicked the video play overlay, the handler could execute arbitrary JavaScript in the viewer's session. Default Content Security Policy settings block inline event handlers, but instances with CSP disabled or relaxed could allow the script to read page content and make authenticated requests as the viewer. This issue is fixed in versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0.
Vulnerability class: XSS (Cross-Site Scripting)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.7 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
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
- github.com/discourse/discourse/security/advisories/GHSA-8m44-f6g9-7cg7
- github.com/discourse/discourse/pull/42882
- github.com/discourse/discourse/commit/05d92b8749f68d2626cbe65ec7adde7562a0283d
- github.com/discourse/discourse/commit/5674b3e6594825c28d2678e55057fd6802f11031
- github.com/discourse/discourse/commit/c3993e318e172389be5c98455177876f1dd87dda
- github.com/discourse/discourse/commit/d7126af3264b672d2201d84c18a37cb8627424a8
Frequently asked questions
- What is CVE-2026-91122?
- CVE-2026-91122 is a high-severity vulnerability in Discourse, classified under Cross-site Scripting. CVSS score: 8.7/10. Published 2026-09-24.
- How severe is CVE-2026-91122?
- High severity. CVSS v3 base score is 8.7 out of 10.