Discourse: Stored HTML injection in video notification emails
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Cross-site scripting
- Confidentiality · integrity · availability
- Low · Low · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA. Impact type from CWE-79.
Summary
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| discourse | discourse | before 2026.8.0; 2026.7.0-latest to before 2026.7.2; 2026.6.0-latest to before 2026.6.3; 2026.1.0-latest to before 2026.1.8 | 2026.8.0, 2026.7.2, 2026.6.3, 2026.1.8 | Patch available | CNA |
- discourse Vendordiscourse Affected before 2026.8.0; 2026.7.0-latest to before 2026.7.2; 2026.6.0-latest to before 2026.6.3; 2026.1.0-latest to before 2026.1.8 Fixed in 2026.8.0, 2026.7.2, 2026.6.3, 2026.1.8 Patch available CNA
Remediation
- Fix · CNA discourse (discourse) Fixed in 2026.8.0, 2026.7.2, 2026.6.3, 2026.1.8
Timeline
- 2026-10-02 Threatist record created from CVE-2026-91120
References
Other 6
- https://github.com/discourse/discourse/security/advisories/GHSA-h7cg-2vww-m45c
- https://github.com/discourse/discourse/pull/42882
- https://github.com/discourse/discourse/commit/6bf1cdcb3ae1aa146e1fd953a62046bf4a1f143f
- https://github.com/discourse/discourse/commit/8338919df4ecbd0fb85314b762772cc033b764e3
- https://github.com/discourse/discourse/commit/e7de8285203a2edf85beff3b951e66aeb7e5dc76
- https://github.com/discourse/discourse/commit/ed8b47df80bcc9f0bd70773fc399c9386f9d52dd
More discourse vulnerabilities
- TI-2022-22806 Discourse BBCode plugin vulnerable to arbitrary CSS injection CVSS 3.1CRITICAL 9.8
- TI-2021-19656 Denial of Service in discourse CVSS 3.1MEDIUM 6.8
- TI-2024-36150 Potential Backup file leaked via Nginx in Discourse CVSS 3.1HIGH 7.5
- TI-2021-18002 RCE via malicious SNS subscription payload CVSS 3.1CRITICAL 10.0
- TI-2026-24651 Discourse: Open redirect via `sso_destination_url` cookie in `enter` CVSS 4.0MEDIUM 5.1
- TI-2022-18730 Discourse Patreon vulnerable to improper validation of email during Patreon authentication CVSS 3.1CRITICAL 9.8
Sources
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences