Vulnerability in Discourse
CVE-2026-72721
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N.
EPSS exploit prediction
EPSS: 0.006 (45.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 46th percentile — 45.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.006 · change: +0.002
Affected products
- Discourse — versions < 2026.1.6, >= 2026.5.0-latest, < 2026.5.2, >= 2026.6.0-latest, < 2026.6.1
Weakness classification (CWE)
References
- github.com/discourse/discourse/commit/a3e10759fef47f03d450649bb51d9e84f4c68b8f
- github.com/discourse/discourse/commit/c2eb6b0e5597d6f28f4be739b83300bc9c69e3cd
- github.com/discourse/discourse/commit/caa615c371b1696982ee11ac8f3558f0f8ced584
- github.com/discourse/discourse/commit/f503971d311b7b0dfdb751ee8cfd67e8cb99f5c5
- 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-24rq-h5j6
Frequently asked questions
- What is CVE-2026-72721?
- CVE-2026-72721 is a medium-severity vulnerability in Discourse, classified under Improper Handling of Case Sensitivity. CVSS score: 5.3/10. Published 2026-08-10.
- How severe is CVE-2026-72721?
- Medium severity. CVSS v3 base score is 5.3 out of 10.