Discourse: Chat MessageBus delivers read-restricted messages to unauthorized users
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- Required
- Attack complexity
- Low
- Impact type
- Cross-site scripting
- Confidentiality · integrity · availability
- High · High · 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, 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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Total
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-2026-91122
References
Other 6
- https://github.com/discourse/discourse/security/advisories/GHSA-8m44-f6g9-7cg7
- https://github.com/discourse/discourse/pull/42882
- https://github.com/discourse/discourse/commit/05d92b8749f68d2626cbe65ec7adde7562a0283d
- https://github.com/discourse/discourse/commit/5674b3e6594825c28d2678e55057fd6802f11031
- https://github.com/discourse/discourse/commit/c3993e318e172389be5c98455177876f1dd87dda
- https://github.com/discourse/discourse/commit/d7126af3264b672d2201d84c18a37cb8627424a8
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