CVE-2026-72721 PUBLISHED

Discourse: Onebox Domain Blocklist Bypass via Case-Sensitive Comparison

Assigner: GitHub_M
Reserved: 10.08.2026 Published: 10.08.2026 Updated: 10.08.2026

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.

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
CVSS Score: 5.3

Attack Vector	Network	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	Low
Privileges Required	None	Integrity Impact	None
User Interaction	None	Availability Impact	None

CVSS 3.1

Product Status

Vendor	discourse
Product	discourse
Versions	Version < 2026.1.6 is affected Version >= 2026.5.0-latest, < 2026.5.2 is affected Version >= 2026.6.0-latest, < 2026.6.1 is affected Version >= 2026.7.0-latest, < 2026.7.0 is affected

References

Problem Types

CWE-178: Improper Handling of Case Sensitivity CWE