Discourse: Onebox Domain Blocklist Bypass via Case-Sensitive Comparison
Priority LOW 31CWE-178Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- —
- Confidentiality · integrity · availability
- Low · None · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA.
Summary
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.
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00585 48th percentileScored 2026-11-07
Fix Fixed discourse (discourse): 2026.1.6, 2026.5.2, 2026.6.1 +1
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- Yes
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| discourse | discourse | before 2026.1.6; 2026.5.0-latest to before 2026.5.2; 2026.6.0-latest to before 2026.6.1; 2026.7.0-latest to before 2026.7.0 | 2026.1.6, 2026.5.2, 2026.6.1, 2026.7.0 | Patch available | CNA |
- discourse Vendordiscourse Affected before 2026.1.6; 2026.5.0-latest to before 2026.5.2; 2026.6.0-latest to before 2026.6.1; 2026.7.0-latest to before 2026.7.0 Fixed in 2026.1.6, 2026.5.2, 2026.6.1, 2026.7.0 Patch available CNA
Remediation
- Fix · CNA discourse (discourse) Fixed in 2026.1.6, 2026.5.2, 2026.6.1, 2026.7.0
Timeline
- 2026-10-02 Threatist record created from CVE-2026-72721
References
Other 9
- https://github.com/discourse/discourse/security/advisories/GHSA-3x7x-24rq-h5j6
- https://github.com/discourse/discourse/pull/42091
- https://github.com/discourse/discourse/pull/42092
- https://github.com/discourse/discourse/pull/42093
- https://github.com/discourse/discourse/pull/42094
- https://github.com/discourse/discourse/commit/a3e10759fef47f03d450649bb51d9e84f4c68b8f
- https://github.com/discourse/discourse/commit/c2eb6b0e5597d6f28f4be739b83300bc9c69e3cd
- https://github.com/discourse/discourse/commit/caa615c371b1696982ee11ac8f3558f0f8ced584
- https://github.com/discourse/discourse/commit/f503971d311b7b0dfdb751ee8cfd67e8cb99f5c5
More discourse vulnerabilities
- TI-2022-22806 Discourse BBCode plugin vulnerable to arbitrary CSS injection CVSS 3.1CRITICAL 9.8
- TI-2021-19656 Denial of Service in discourse CVSS 3.1MEDIUM 6.8
- TI-2024-36150 Potential Backup file leaked via Nginx in Discourse CVSS 3.1HIGH 7.5
- TI-2021-18002 RCE via malicious SNS subscription payload CVSS 3.1CRITICAL 10.0
- TI-2026-24651 Discourse: Open redirect via `sso_destination_url` cookie in `enter` CVSS 4.0MEDIUM 5.1
- TI-2022-18730 Discourse Patreon vulnerable to improper validation of email during Patreon authentication CVSS 3.1CRITICAL 9.8
Sources
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences