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.

No CVSS v4.0

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact Low

Integrity Impact None

Availability Impact None

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Exploitation none

Automatable yes

Technical Impact partial

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
discourse discourse affected
Version Status Constraints
< 2026.1.6 affected —
>= 2026.5.0-latest, < 2026.5.2 affected —
>= 2026.6.0-latest, < 2026.6.1 affected —
>= 2026.7.0-latest, < 2026.7.0 affected —

No data.

No data.

No data.

Project Subscriptions

No data.

Advisories

No advisories yet.

Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

References
Link Providers
https://github.com/discourse/discourse/commit/a3e10759fef47f03d450649bb51d9e84f4c68b8f cve-icon
https://github.com/discourse/discourse/commit/c2eb6b0e5597d6f28f4be739b83300bc9c69e3cd cve-icon
https://github.com/discourse/discourse/commit/caa615c371b1696982ee11ac8f3558f0f8ced584 cve-icon
https://github.com/discourse/discourse/commit/f503971d311b7b0dfdb751ee8cfd67e8cb99f5c5 cve-icon
https://github.com/discourse/discourse/pull/42091 cve-icon
https://github.com/discourse/discourse/pull/42092 cve-icon
https://github.com/discourse/discourse/pull/42093 cve-icon
https://github.com/discourse/discourse/pull/42094 cve-icon
https://github.com/discourse/discourse/security/advisories/GHSA-3x7x-24rq-h5j6 cve-icon
History

Mon, 10 Aug 2026 17:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Mon, 10 Aug 2026 16:15:00 +0000

Type Values Removed Values Added
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.
Title Discourse: Onebox Domain Blocklist Bypass via Case-Sensitive Comparison
Weaknesses CWE-178
References
Metrics cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-08-10T16:59:07.554Z

Reserved: 2026-08-10T13:48:09.545Z

Link: CVE-2026-72721

cve-icon Vulnrichment

Updated: 2026-08-10T16:59:02.627Z

cve-icon NVD

No data.

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses