CVE-2026-73309
XenForo < 2.3.13 Authentication Bypass via OAuth2 Token Endpoint
CVSS Score
7.4
EPSS Score
0.0%
EPSS Percentile
0th
XenForo before 2.3.13 contains an authentication bypass vulnerability in the OAuth2 token endpoint that allows unauthenticated attackers to obtain valid token pairs by submitting empty values for client_secret and code_verifier parameters. Attackers can exploit PHP truthy evaluation logic, which treats empty strings as false and skips client secret validation and PKCE code verifier validation, to exchange a valid authorization code for a token pair without proving client identity or holding the PKCE commitment.
| CWE | CWE-697 |
| Vendor | xenforo |
| Product | xenforo |
| Published | Sep 8, 2026 |
| Last Updated | Sep 9, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None
Affected Versions
XenForo / XenForo
0 < 2.3.13
References
xenforo.com: https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/ xenforo.com: https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/ bombobombone.github.io: https://bombobombone.github.io/posts/cve-2026-73309/ github.com: https://github.com/BomboBombone/CVE-2026-73309 vulncheck.com: https://www.vulncheck.com/advisories/xenforo-authentication-bypass-via-oauth2-token-endpoint
Credits
Marco Paciaroni (BomboBombone) VulnCheck