# CVE-2026-91120: Discourse HTML injection in lazy video embed notifications

Source: https://junglewise.ai/threats/cve-2026-91120-discourse-is-an-open-source-discussion-platform-prior-to-2026-1-8  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-24. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-91120 · Severity: medium · CVSS 5.4 · Published 2026-09-24

Discourse is an open-source discussion platform that allows users to embed videos from YouTube, Vimeo, and TikTok. When lazy video loading is enabled (the default), malicious video titles containing HTML markup are not properly escaped before being included in notification emails and chat summaries. A user with standard posting privileges can exploit this to inject HTML content, including event handlers, into emails received by other users, potentially leading to credential theft or malware delivery if recipients use HTML-capable email clients.

Technologies: [Discourse](https://junglewise.ai/threats/technologies/discourse). Vendors: [Discourse](https://junglewise.ai/threats/vendors/discourse).

## Quick answers

**Is CVE-2026-91120 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-91120 being exploited in the wild.

**How severe is CVE-2026-91120?** Medium severity, with a CVSS score of 5.4, published 24 September 2026.

**Which products and versions are affected?** Discourse Before 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0.

**Is there a fix for CVE-2026-91120?** A patch was published on 2026-08-25: Fix committed to repository; versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0 contain the patch Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-91120 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-91120?** Check whether you run Discourse at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability is a stored HTML injection in the lazy video embed rendering path affecting notification emails and chat summaries. Provider-controlled video titles (from YouTube, Vimeo, or TikTok metadata) were inserted directly into email HTML without escaping. The fix applies HTML entity encoding (ERB::Util.html_escape) to the title field before template rendering. Requires lazy video embeds enabled (default), standard user posting privileges, and target users receiving notification emails.

## Affected products

- Discourse Discourse Before 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0

## Timeline

- 2026-09-24: disclosed
- 2026-08-25: patched: Fix committed to repository; versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0 contain the patch

## References

- [https://github.com/discourse/discourse/commit/6bf1cdcb3ae1aa146e1fd953a62046bf4a1f143f](https://github.com/discourse/discourse/commit/6bf1cdcb3ae1aa146e1fd953a62046bf4a1f143f)
- [https://github.com/discourse/discourse/commit/8338919df4ecbd0fb85314b762772cc033b764e3](https://github.com/discourse/discourse/commit/8338919df4ecbd0fb85314b762772cc033b764e3)

## Related threats

- [Discourse reflected cross-site scripting in email unsubscribe](https://junglewise.ai/threats/cve-2017-20290-discourse-1-9-0-beta2-before-1-9-0-beta13-contains-a-reflected)
- [Discourse oEmbed HTML injection in iframe allowlist](https://junglewise.ai/threats/cve-2026-91159-discourse-is-an-open-source-discussion-platform-prior-to-2026-9-0)
- [Discourse insufficient upload security metadata reconciliation](https://junglewise.ai/threats/cve-2026-91157-discourse-is-an-open-source-discussion-platform-prior-to-2026-9-0)
- [Discourse HTML injection in chat message excerpts](https://junglewise.ai/threats/cve-2026-91121-discourse-is-an-open-source-discussion-platform-prior-to-2026-1-8)
- [Discourse stored HTML injection in activity log components](https://junglewise.ai/threats/cve-2026-91119-discourse-is-an-open-source-discussion-platform-prior-to-2026-1-8)