CVE-2026-59830: Discourse: Stored XSS via unescaped actor name in post actions

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-21 · updated 2026-09-23
Weakness: CWE-79

Description

Discourse is an open-source discussion platform. Prior to 2026.7.0, the post action component failed to escape user-controlled display names before interpolating them into an HTML string passed to trustHTML. A user who could choose a crafted display name could persist markup in post action descriptions. Viewing the affected user activity streams could execute attacker-controlled script in another user's browser. This issue is fixed in version 2026.7.0.

Affected products

discourse: before 2026.7.0

References

https://github.com/discourse/discourse/commit/dd786594ddd088657a7e6f9fefba5bd889965fe4
https://github.com/discourse/discourse/releases/tag/v2026.7.0
https://github.com/discourse/discourse/security/advisories/GHSA-x6mf-p7cg-69rw

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