Description
Discourse is an open-source discussion platform. Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0, the topic small-action and nested-activity-log components interpolated the free-form action_code_who value into mention-link href attributes without URL encoding. A quote-bearing display name could terminate the intended URL attribute and inject attacker-controlled elements into the trusted rendered markup. Although the visible mention text was escaped, the unencoded path component allowed stored HTML injection when another user viewed the affected topic action or activity log. This issue is fixed in versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0.
References6
- github.com/discourse/discourse/commit/20dbf112760eb1d6a58f2e49a…
- github.com/discourse/discourse/commit/66653c484cfb91bc346f9a326…
- github.com/discourse/discourse/commit/77a81c7a3a7ff9e94b355e32b…
- github.com/discourse/discourse/commit/c4748f651d9d2f3a6dd3106a4…
- github.com/discourse/discourse/pull/42882
- github.com/discourse/discourse/security/advisories/GHSA-pv3p-p3…
Metrics
- CVSS 3.1
-
6.4
MEDIUM
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N - EPSS — exploit probability
- 0% percentile: 10 · as of 9 November 2026
- CWE
- CWE-79
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.