Discourse 2026 Lazy Video Title XSS in Email/Chat (pre2026.1.8)
CVE-2026-91120 Published on September 24, 2026
Discourse: Stored HTML injection in video notification emails
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.
Vulnerability Analysis
CVE-2026-91120 is exploitable with network access, and requires 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 small 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-2026-91120 has been classified to as a XSS vulnerability or weakness.
Products Associated with CVE-2026-91120
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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.