CVE-2023-43659: Cross-site Scripting via email preview when CSP disabled in Discourse

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-10-16 · updated 2026-06-17
Weakness: CWE-79

Description

Discourse is an open source platform for community discussion. Improper escaping of user input allowed for Cross-site Scripting attacks via the digest email preview UI. This issue only affects sites with CSP disabled. This issue has been patched in the 3.1.1 stable release as well as the 3.2.0.beta1 release. Users are advised to upgrade. Users unable to upgrade should ensure CSP is enabled on the forum.

Affected products

discourse: through 3.1.1; 3.2.0-beta1

References

https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP
https://github.com/discourse/discourse/security/advisories/GHSA-g4qg-5q2h-m8ph
https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP
https://github.com/discourse/discourse/security/advisories/GHSA-g4qg-5q2h-m8ph

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