Description
Discourse is an open-source discussion platform. Prior to 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0, Onebox::DomainChecker.is_blocked? compares hostnames and SiteSetting.blocked_onebox_domains entries case-sensitively, allowing an attacker to bypass configured Onebox domain restrictions by changing character casing in a redirect target hostname. This issue is fixed in versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0.
References9
- github.com/discourse/discourse/commit/a3e10759fef47f03d450649bb…
- github.com/discourse/discourse/commit/c2eb6b0e5597d6f28f4be739b…
- github.com/discourse/discourse/commit/caa615c371b1696982ee11ac8…
- github.com/discourse/discourse/commit/f503971d311b7b0dfdb751ee8…
- github.com/discourse/discourse/pull/42091
- github.com/discourse/discourse/pull/42092
- github.com/discourse/discourse/pull/42093
- github.com/discourse/discourse/pull/42094
- github.com/discourse/discourse/security/advisories/GHSA-3x7x-24…
Metrics
- CVSS 3.1
-
5.3
MEDIUM
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N - EPSS — exploit probability
- 1% percentile: 48 · as of 12 November 2026
- CWE
- CWE-178
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.