# CVE-2026-72721

## Summary

- **CVE ID:** CVE-2026-72721
- **Severity:** MEDIUM
- **CVSS Score:** 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N)
- **CWE:** CWE-178
- **Published:** Aug 10, 2026
- **Last Modified:** Aug 10, 2026

## 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.

## Affected Products

- discourse — discourse (< 2026.1.6)
- discourse — discourse (>= 2026.5.0-latest, < 2026.5.2)
- discourse — discourse (>= 2026.6.0-latest, < 2026.6.1)
- discourse — discourse (>= 2026.7.0-latest, < 2026.7.0)

## References

- [CNA](https://github.com/discourse/discourse/security/advisories/GHSA-3x7x-24rq-h5j6)
- [CNA](https://github.com/discourse/discourse/pull/42091)
- [CNA](https://github.com/discourse/discourse/pull/42092)
- [CNA](https://github.com/discourse/discourse/pull/42093)
- [CNA](https://github.com/discourse/discourse/pull/42094)
- [CNA](https://github.com/discourse/discourse/commit/a3e10759fef47f03d450649bb51d9e84f4c68b8f)
- [CNA](https://github.com/discourse/discourse/commit/c2eb6b0e5597d6f28f4be739b83300bc9c69e3cd)
- [CNA](https://github.com/discourse/discourse/commit/caa615c371b1696982ee11ac8f3558f0f8ced584)
- [CNA](https://github.com/discourse/discourse/commit/f503971d311b7b0dfdb751ee8cfd67e8cb99f5c5)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.43%
- **EPSS Percentile:** 36.0

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._