Discourse up to 2026.1.7/2026.6.2/2026.7.1 cross site scripting

Summaryinfo

A vulnerability marked as problematic has been reported in Discourse up to 2026.1.7/2026.6.2/2026.7.1. Affected by this vulnerability is an unknown functionality. This manipulation causes cross site scripting. This vulnerability is handled as CVE-2026-91120. The attack can be initiated remotely. There is not any exploit available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in Discourse up to 2026.1.7/2026.6.2/2026.7.1. It has been declared as problematic. Affected by this vulnerability is an unknown code. The manipulation with an unknown input leads to a cross site scripting vulnerability. The CWE definition for the vulnerability is CWE-79. The product 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. As an impact it is known to affect integrity. The summary by CVE is:

Discourse is an open-source discussion platform. Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0, provider-controlled video titles in lazy video embeds could be reparsed as HTML when Discourse generated notification emails or chat summaries. A user with standard posting privileges could create a post for an enabled YouTube, Vimeo, or TikTok provider whose title contained markup, and the email and chat-summary rendering path would place that markup into the output instead of treating it solely as text. Recipients using HTML-capable email clients could see injected content, potentially including event handlers, but the issue did not directly expose a Discourse browser session or affect the forum page itself. Lazy video embeds must be enabled, which is the default configuration. This issue is fixed in versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-91120 since 09/14/2026. The exploitation appears to be easy. The attack can be launched remotely. It demands that the victim is doing some kind of user interaction. The technical details are unknown and an exploit is not publicly available. The attack technique deployed by this issue is T1059.007 according to MITRE ATT&CK.

Upgrading to version 2026.1.8, 2026.6.3, 2026.7.2 or 2026.8.0 eliminates this vulnerability.

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Productinfo

Type

• Chat Software

Name

• Discourse

Version

• 2026.1.0
• 2026.1.1
• 2026.1.2
• 2026.1.3
• 2026.1.4
• 2026.1.5
• 2026.1.6
• 2026.1.7
• 2026.6.0
• 2026.6.1
• 2026.6.2
• 2026.7.0
• 2026.7.1

License

• open-source

Website

• Product: https://github.com/discourse/discourse/

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