Discourse: Chat upload filenames rendered as raw HTML in excerpts
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Cross-site scripting
- Confidentiality · integrity · availability
- None · 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, attacker-controlled upload filenames used in chat message excerpts were rendered as unescaped HTML. A user able to upload a file and send chat content could place markup in a filename that was then interpreted by chat channel lists, chat summary emails, pinned message bars, reply previews, thread previews, and other excerpt renderers. The issue allowed trusted-HTML injection that altered rendered excerpt content, but JavaScript execution was not demonstrated with default Content Security Policy settings. The advisory states that no confidentiality, integrity, or availability impact was identified, while its structured scoring metadata separately assigns low integrity impact. Sites that disable or relax the default CSP have increased exposure. 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-2026-91121
References
Other 6
- https://github.com/discourse/discourse/security/advisories/GHSA-34rh-wjfv-65gq
- https://github.com/discourse/discourse/pull/42882
- https://github.com/discourse/discourse/commit/24cd7cc4c868f20e6037d67d801d60c3e289b278
- https://github.com/discourse/discourse/commit/6e7a181909c34a059d2b0a6291335a363205b787
- https://github.com/discourse/discourse/commit/9d6f5e64a1cb68e8208520e4209b361e14f7394b
- https://github.com/discourse/discourse/commit/af197941f7613a3845cba21d217641c77c8ef836
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