Vulnerability 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.
CVSS Score
MEDIUM
Related Weaknesses (CWE)
References
- https://github.com/discourse/discourse/commit/a3e10759fef47f03d450649bb51d9e84f4
- https://github.com/discourse/discourse/commit/c2eb6b0e5597d6f28f4be739b83300bc9c
- https://github.com/discourse/discourse/commit/caa615c371b1696982ee11ac8f3558f0f8
- https://github.com/discourse/discourse/commit/f503971d311b7b0dfdb751ee8cfd67e8cb
- https://github.com/discourse/discourse/pull/42091
- https://github.com/discourse/discourse/pull/42092
- https://github.com/discourse/discourse/pull/42093
- https://github.com/discourse/discourse/pull/42094
- https://github.com/discourse/discourse/security/advisories/GHSA-3x7x-24rq-h5j6
FAQ
What is CVE-2026-72721?
CVE-2026-72721 is a vulnerability with a CVSS score of 5.3 (MEDIUM). 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 entrie...
How severe is CVE-2026-72721?
CVE-2026-72721 has been rated MEDIUM with a CVSS base score of 5.3/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-72721?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.