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CVE-2026-73309 Details

Description

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.

Metrics

CVSS 3.x Severity and Vector Strings:

NIST: [email protected]CVSS-B:9.1 CRITICALVector:CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

CNA: [email protected]CVSS-B:7.4 HIGHVector:CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

References to Advisories, Solutions, and Tools

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URL	Source(s)	Tag(s)
https://bombobombone.github.io/posts/cve-2026-73309/	[email protected]	ExploitThird Party Advisory
https://github.com/BomboBombone/CVE-2026-73309	[email protected]	Third Party Advisory
https://www.vulncheck.com/advisories/xenforo-authentication-bypass-via-oauth2-token-endpoint	[email protected]	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/	[email protected]	Release Notes
https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/	[email protected]	Release Notes

Weakness Enumeration

CWE-ID	CWE Name	Source
CWE-697	Incorrect Comparison	[email protected]

Affected Products

Product	Versions
xenforo xenforo	< 2.3.13
CPE cpe:2.3:a:xenforo:xenforo:::::::: Remediation No remediation found in references.

Change History

4 change records found show changes

Date	Action	Recorded By
Sep 11, 2026	Initial Analysis	[email protected]
Sep 9, 2026	CVE Modified	CISA-ADP
Sep 9, 2026	CVE Modified	[email protected]
Sep 8, 2026	New CVE Received	[email protected]