Discourse: Encode action_code_who in mention URLs
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, the topic small-action and nested-activity-log components interpolated the free-form action_code_who value into mention-link href attributes without URL encoding. A quote-bearing display name could terminate the intended URL attribute and inject attacker-controlled elements into the trusted rendered markup. Although the visible mention text was escaped, the unencoded path component allowed stored HTML injection when another user viewed the affected topic action or activity log. 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-2026-91119
References
Other 6
- https://github.com/discourse/discourse/security/advisories/GHSA-pv3p-p3m9-v8v3
- https://github.com/discourse/discourse/pull/42882
- https://github.com/discourse/discourse/commit/20dbf112760eb1d6a58f2e49aeef7546898b6f1c
- https://github.com/discourse/discourse/commit/66653c484cfb91bc346f9a326f6945387f17b035
- https://github.com/discourse/discourse/commit/77a81c7a3a7ff9e94b355e32b8f379f2d389e05a
- https://github.com/discourse/discourse/commit/c4748f651d9d2f3a6dd3106a4d5564536c645168
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