Medium 5.3Published Aug 10, 2026

CVE-2026-72721Discourse: Onebox Domain Blocklist Bypass via Case-Sensitive Comparison

Updated under an hour ago (Oct 28, 2026, 10:23 AM ET)

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No exploitation reported and no EPSS estimate yet.

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Exploited in the last 30 days

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: 5.3 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Weakness (CWE): CWE-178
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Deferred
Record last updated: Aug 10, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

discourse discourse discourse:discourse (from the name)	before 2026.1.6; from 2026.5.0-latest, < 2026.5.2; from 2026.6.0-latest, < 2026.6.1; from 2026.7.0-latest, < 2026.7.0	CNA record

References

References

https://github.com/discourse/discourse/security/advisories/GHSA-3x7x-24rq-h5j6	x-refsource-confirm
https://github.com/discourse/discourse/pull/42091	x-refsource-misc
https://github.com/discourse/discourse/pull/42092	x-refsource-misc
https://github.com/discourse/discourse/pull/42093	x-refsource-misc
https://github.com/discourse/discourse/pull/42094	x-refsource-misc
https://github.com/discourse/discourse/commit/a3e10759fef47f03d450649bb51d9e84f4c68b8f	x-refsource-misc
https://github.com/discourse/discourse/commit/c2eb6b0e5597d6f28f4be739b83300bc9c69e3cd	x-refsource-misc
https://github.com/discourse/discourse/commit/caa615c371b1696982ee11ac8f3558f0f8ced584	x-refsource-misc
https://github.com/discourse/discourse/commit/f503971d311b7b0dfdb751ee8cfd67e8cb99f5c5	x-refsource-misc

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.