CVE-2026-91121Discourse: Chat upload filenames rendered as raw HTML in excerpts
- 5.0MediumCVSS base score
- 0.26%Exploitation in 30 daysEPSS · top 82% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
Description
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.
Timeline
ID reserved
By GitHub_M
- 10 days later
· 10 days later
Published
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_MCNA (assigner) | 3.1 | Medium5.0 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:N |
| NVDNVD · Deferred | 3.1 | Medium5.0 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:N |
- EPSS (exploitation in 30 days)
- 0.26% · top 82% of all CVEs (13 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.0.
Affected products
References
References6
- https://github.com/discourse/discourse/security/advisories/GHSA-34rh-wjfv-65gq (opens in a new tab)x_refsource_CONFIRM
- https://github.com/discourse/discourse/pull/42882 (opens in a new tab)x_refsource_MISC
- https://github.com/discourse/discourse/commit/24cd7cc4c868f20e6037d67d801d60c3e289b278 (opens in a new tab)x_refsource_MISC
- https://github.com/discourse/discourse/commit/6e7a181909c34a059d2b0a6291335a363205b787 (opens in a new tab)x_refsource_MISC
- https://github.com/discourse/discourse/commit/9d6f5e64a1cb68e8208520e4209b361e14f7394b (opens in a new tab)x_refsource_MISC
- https://github.com/discourse/discourse/commit/af197941f7613a3845cba21d217641c77c8ef836 (opens in a new tab)x_refsource_MISC
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-86306 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2026-91121)Record last updated .