Medium severity · published Aug 10, 2026
CVE-2026-72721
Discourse: Onebox Domain Blocklist Bypass via Case-Sensitive Comparison
5.3
CVSS
0.6%
EPSS
No
On KEV
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 vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
Low
Integrity
None
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.6% · higher than 48% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
DI
discourse · discourse
< 2026.1.6; >= 2026.5.0-latest, < 2026.5.2; >= 2026.6.0-latest, < 2026.6.1; >= 2026.7.0-latest, < 2026.7.0 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-72721
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-72721
github.com
https://github.com/discourse/discourse/commit/a3e10759fef47f03d450649bb51d9e84f4c68b8f
github.com
https://github.com/discourse/discourse/commit/c2eb6b0e5597d6f28f4be739b83300bc9c69e3cd
github.com
https://github.com/discourse/discourse/commit/caa615c371b1696982ee11ac8f3558f0f8ced584
github.com
https://github.com/discourse/discourse/commit/f503971d311b7b0dfdb751ee8cfd67e8cb99f5c5
github.com
https://github.com/discourse/discourse/pull/42091
github.com
https://github.com/discourse/discourse/pull/42092
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