CVE-2026-72721
Received Received - Intake

Case-Insensitive Onebox Domain Bypass in Discourse

Publication date: 2026-08-10

Last updated on: 2026-08-10

Assigner: GitHub, Inc.

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.

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Meta Information

Published
2026-08-10
Last Modified
2026-08-10
Generated
2026-08-10
AI Q&A
2026-08-10
EPSS Evaluated
N/A
NVD
CVE-2026-72721
EUVD
EUVD-2026-55657

Affected Vendors & Products

Showing 4 associated CPEs
Vendor Product Version / Range
discourse discourse to 2026.1.6 (exc)
discourse discourse to 2026.5.2 (exc)
discourse discourse to 2026.6.1 (exc)
discourse discourse to 2026.7.0 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-178 The product does not properly account for differences in case sensitivity when accessing or determining the properties of a resource, leading to inconsistent results.

Attack-Flow Graph

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Executive Summary

This vulnerability affects Discourse, an open-source discussion platform. It allows attackers to bypass domain restrictions for Onebox embeds by changing the case of characters in a redirect target hostname. The issue occurs because the system compares hostnames and blocked domains case-sensitively, which is insufficient for security.

Impact Analysis

An attacker could exploit this to bypass domain restrictions and embed malicious or unauthorized content via Onebox. This could lead to phishing attacks, unauthorized data access, or other security risks depending on how Onebox is used in your Discourse instance.

Mitigation Strategies

Update Discourse to version 2026.1.6, 2026.5.2, 2026.6.1, or 2026.7.0 or later to fix the case-sensitive Onebox domain restriction bypass.

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