Discourse: Onebox Domain Blocklist Bypass via Case-Sensitive Comparison
13Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 5.3epss 0.4%
exploitation probability
0.4%top 63% of all CVEs
observed exploitation
nono source reports it
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.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Affected products
discourse · discourseReferences
https://github.com/discourse/discourse/commit/a3e10759fef47f03d450649bb51d9e84f4c68b8fhttps://github.com/discourse/discourse/commit/c2eb6b0e5597d6f28f4be739b83300bc9c69e3cdhttps://github.com/discourse/discourse/commit/caa615c371b1696982ee11ac8f3558f0f8ced584https://github.com/discourse/discourse/commit/f503971d311b7b0dfdb751ee8cfd67e8cb99f5c5https://github.com/discourse/discourse/pull/42091https://github.com/discourse/discourse/pull/42092https://github.com/discourse/discourse/pull/42093https://github.com/discourse/discourse/pull/42094https://github.com/discourse/discourse/security/advisories/GHSA-3x7x-24rq-h5j6