XenForo up to 2.3.12 OAuth2 Token Endpoint client_secret/code_verifier improper authorization

Summaryinfo

A vulnerability has been found in XenForo up to 2.3.12 and classified as critical. This impacts an unknown function of the component OAuth2 Token Endpoint. The manipulation of the argument client_secret/code_verifier leads to improper authorization. This vulnerability is referenced as CVE-2026-73309. Remote exploitation of the attack is possible. No exploit is available.

Detailsinfo

A vulnerability was found in XenForo up to 2.3.12. It has been rated as critical. This issue affects an unknown part of the component OAuth2 Token Endpoint. The manipulation of the argument client_secret/code_verifier with an unknown input leads to a improper authorization vulnerability. Using CWE to declare the problem leads to CWE-285. The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at xenforo.com. The identification of this vulnerability is CVE-2026-73309 since 08/11/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1548.002 according to MITRE ATT&CK.

Upgrading to version 2.3.13 eliminates this vulnerability.

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Productinfo

Name

• XenForo

Version

• 2.3.0
• 2.3.1
• 2.3.2
• 2.3.3
• 2.3.4
• 2.3.5
• 2.3.6
• 2.3.7
• 2.3.8
• 2.3.9
• 2.3.10
• 2.3.11
• 2.3.12

CPE 2.3info

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CPE 2.2info

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