CVE-2026-91122 Discourse: Chat MessageBus delivers read-restricted messages to unauthorized users
Authenticated users can inject JavaScript via video placeholders, potentially executing code in other users' sessions if CSP is disabled.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-91122?
CVE-2026-91122 is a high-severity cross-site scripting vulnerability in discourse, published on 24 Sep 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official description
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.
Weakness: CWE-79
Which versions are affected by CVE-2026-91122?
1 open source package ship an affected version, including discourse.
| Package | Affected | Fixed in |
|---|---|---|
discourse Bitnami | All versions | 2026.8.0 |
How do I fix CVE-2026-91122?
Upgrade discourse to 2026.8.0 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-91122 being exploited?
There is no known exploitation of CVE-2026-91122 in the wild and no public exploit code.
Sources
Also known as BIT-discourse-2026-91122, GHSA-8m44-f6g9-7cg7.