CVE-2026-23743
Published: 28 January 2026
Summary
CVE-2026-23743 is a medium-severity Exposure of Sensitive Information to an Unauthorized Actor (CWE-200) vulnerability in Discourse Discourse. Its CVSS base score is 6.9 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 22.2th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 AC-3 (Access Enforcement) and SI-11 (Error Handling).
Deeper analysis
CVE-2026-23743 is an information disclosure vulnerability in Discourse, an open source discussion platform. It affects versions prior to 3.5.4, 2025.11.2, 2025.12.1, and 2026.1.0. Specifically, permalinks pointing to access-restricted resources—such as private topics, categories, posts, or hidden tags—redirect users without access to URLs containing the resource slug. This leaks potentially sensitive information, like private topic titles, through the redirect Location header and the 404 page's search box. The issue is classified as CWE-200 with a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N).
Any unauthenticated attacker with network access can exploit this vulnerability with low complexity and no user interaction. By requesting permalinks to restricted resources—through guessing, enumeration, or external referrals—attackers can extract sensitive metadata from the redirect responses or 404 pages, enabling reconnaissance of private content structures and titles that should remain hidden.
The vulnerability is patched in Discourse versions 3.5.4, 2025.11.2, 2025.12.1, and 2026.1.0, as detailed in the GitHub security advisory at https://github.com/discourse/discourse/security/advisories/GHSA-v5jw-rxc6-4cvv. No known workarounds are available.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-4861
Vulnerability details
Discourse is an open source discussion platform. In versions prior to 3.5.4, 2025.11.2, 2025.12.1, and 2026.1.0, permalinks pointing to access-restricted resources (private topics, categories, posts, or hidden tags) were redirecting users to URLs containing the resource slug, even when the…
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user didn't have access to view the resource. This leaked potentially sensitive information (e.g., private topic titles) via the redirect Location header and the 404 page's search box. This issue is patched in versions 3.5.4, 2025.11.2, 2025.12.1, and 2026.1.0. No known workarounds are available.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Direct exploitation of public-facing Discourse web app via crafted permalink requests to leak restricted resource metadata (titles, slugs).
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Enforces approved authorizations for access to restricted resources, preventing redirects and error pages from leaking sensitive slugs or titles to unauthorized users.
Handles errors and exceptions, such as 404 pages for restricted permalinks, without disclosing sensitive information like private topic titles.
Filters system outputs including HTTP redirect Location headers and 404 page content to block transmission of sensitive resource metadata.