CVE-2026-73309

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.

CVSS v3 7.4 HIGH

7.4^/10

CVSS v3 : HIGH

Vector :

Exploitability : 2.2 / Impact : 5.2

Attack Vector NETWORK

Attack Complexity HIGH

Privileges Required NONE

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact HIGH

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://bombobombone.github.io/posts/cve-2026-73309/	Exploit Third Party Advisory
https://github.com/BomboBombone/CVE-2026-73309	Third Party Advisory
https://www.vulncheck.com/advisories/xenforo-authentication-bypass-via-oauth2-token-endpoint	Third Party Advisory
https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/	Release Notes
https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/	Release Notes

Configurations

Configuration 1 (hide)

cpe:2.3:a:xenforo:xenforo:*:*:*:*:*:*:*:*

History

No history.

Information

Published : 2026-09-08 14:17

Updated : 2026-09-11 20:33

NVD link : CVE-2026-73309

Mitre link : CVE-2026-73309

CVE.ORG link : CVE-2026-73309

JSON object : View

Products Affected

xenforo

xenforo

CWE

CWE-697

Incorrect Comparison

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