CVE-2026-72721

MEDIUM

5.3

CVSS v3

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.

CWE-178

How to fix

No published remediation has been found for this vulnerability's affected products yet.

Mitigation guidance may be in the linked vendor advisories in the References section below.

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CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityLow

IntegrityNone

AvailabilityNone

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

Exploit Intelligence

EPSS data unavailable for this CVE.

References

Other references9

Related Vulnerabilities

Other CWE-178 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2025-27636	Medium	5.6	81%	-	Fix
CVE-2021-24347	High	8.8	54%	-	Fix
CVE-2020-12812	Critical	9.8	49%	KEV + Ransom	Fix
CVE-2003-0411	High	7.5	25%	-	-
CVE-2018-9845	Critical	9.8	13%	-	Fix
CVE-2001-0766	Critical	9.8	8.2%	-	-

Common questions

How do I fix CVE-2026-72721?

No published fix for CVE-2026-72721 has been found yet. Check the linked vendor advisories for guidance as it becomes available.

How severe is CVE-2026-72721?

CVE-2026-72721 has a CVSS v3 base score of 5.3, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-08-10.