What’s Vulnerable › Vulnerabilities

CVE-2026-72722: Discourse: Duplicate lookup reveals restricted topic titles through canonicalized URLs

• Severity: medium (CVSS 4.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-10 · updated 2026-09-08
• Weakness: CWE-862

Description

Discourse is an open-source discussion platform. Prior to 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0, TopicLink.extract_from, TopicLink.ensure_entry_for, and TopicLink.duplicate_lookup do not consistently enforce Guardian.can_see? checks when processing internal links. An authenticated user can submit links to restricted topics, private messages, or hidden posts and receive canonicalized slugs or titles in the composer_messages duplicate_lookup response even though the targets are not visible to that user. This issue is fixed in versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0.

Affected products

• discourse: before 2026.1.6; from 2026.5.0-latest, < 2026.5.2; from 2026.6.0-latest, < 2026.6.1; from 2026.7.0-latest, < 2026.7.0

References

• https://github.com/discourse/discourse/commit/45abd925e46e8be40d2d047bced26628f26e4e31
• https://github.com/discourse/discourse/commit/7d7ce546ac86e24a6512b321ace69fc52fe37bf4
• https://github.com/discourse/discourse/commit/836a251d54a1004fb1c463a7d299b933b176191f
• https://github.com/discourse/discourse/commit/e54ba27eacee0f14f315e510e287e7ac2e4bdb1a
• 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/security/advisories/GHSA-4fx9-5m29-83p4

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