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CVE-2026-73309

9.1, critical

XenForo before 2.3.13 contains an authentication bypass vulnerability in the OAuth2 token endpoint that allows unauthenticated attackers…

NVD (opens in a new tab) CVE.org (opens in a new tab)
CVSS
9.1, critical critical CVSS v3.1
EPSS, next 30 days
0.7% higher than 51.6% of scored CVEs
Exploitation
Exploit code published
Published
8 Sept 2026a month ago

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.

Details

Vendor
XenForo
Product
XenForo
Weakness
CWE-697 (opens in a new tab)
Status
Analyzed
Updated
11 Sept 2026
Assigner
disclosure@vulncheck.com

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

References 5

Exploit code 1

Advisories 4

The kind is read from NVD's tags where present and from the shape of the URL otherwise, so treat it as a hint.

Other XenForo CVEs

Every XenForo CVE we hold

Same vendor in what we hold, not a known link between the flaws.

  • CVE-2026-73313 XenForo Incorrect Authorization Vulnerability EPSS 0.6% 8.1, high

Beyond this page

Is CVE-2026-73309 in your network?

This page tells you how dangerous CVE-2026-73309 is out there. Whether it sits on one of your devices, only a scan of your own network can tell. That is what our systems do, every day, for the companies we protect.

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Check your exposure

Assembled from the NVD 2.0 API, the CISA Known Exploited Vulnerabilities Catalog and FIRST EPSS. Scores are as of our last collection on 17 Oct 2026, not the live upstream state.