Discourse Video Placeholder XSS via Injected Event Handler (pre-2026.1.8)
CVE-2026-91122 Published on September 24, 2026
Discourse: Chat MessageBus delivers read-restricted messages to unauthorized users
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 Analysis
CVE-2026-91122 is exploitable with network access, requires user interaction and a small amount of user privileges. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have a high impact on confidentiality and integrity, and no impact on availability.
Weakness Type
What is a XSS Vulnerability?
The software does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
CVE-2026-91122 has been classified to as a XSS vulnerability or weakness.
Products Associated with CVE-2026-91122
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Affected Versions
discourse:- Version < 2026.8.0 is affected.
- Version >= 2026.7.0-latest, < 2026.7.2 is affected.
- Version >= 2026.6.0-latest, < 2026.6.3 is affected.
- Version >= 2026.1.0-latest, < 2026.1.8 is affected.