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Vulnerability record · CVE-2026-73311 · published 8 September 2026

CVE-2026-73311: Xenforo authentication bypass by capture-replay vulnerability

Xenforo · Xenforo

XenForo before 2.3.13 contains an OAuth2 authorization code reuse vulnerability that allows attackers to obtain unauthorized token pairs by submitting a previously used authorization code. Attackers can exploit the failure to invalidate or mark authorization codes as consumed after initial token issuance to receive an independent token pair for the same user and scopes, bypassing the single-use guarantee of the OAuth2 authorization code flow.

9.1 CVSS 4.0 Critical EPSS 0.50% · top 59.8% CWE-294 · Authentication bypass by capture-replay
9.1CVSS 4.0 base score
0.50%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
5References, 2 tagged exploit
11 Sep 2026Last modified by NVD

Description

XenForo before 2.3.13 contains an OAuth2 authorization code reuse vulnerability that allows attackers to obtain unauthorized token pairs by submitting a previously used authorization code. Attackers can exploit the failure to invalidate or mark authorization codes as consumed after initial token issuance to receive an independent token pair for the same user and scopes, bypassing the single-use guarantee of the OAuth2 authorization code flow.

CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://bombobombone.github.io/posts/cve-2026-73311/ ExploitThird Party Advisory
https://github.com/BomboBombone/CVE-2026-73311 ExploitThird Party Advisory
https://www.vulncheck.com/advisories/xenforo-oauth2-authorization-code-reuse Third Party Advisory
https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.23 Release Notes
https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/ Release Notes

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.3CVE-2025-71279Xenforo improper authentication vulnerabilityXenForo before 2.3.7 contains a security issue affecting Passkeys that have been added to user accounts. An attacker may be able to compromise the se…EPSS 0.45%9.1CVE-2026-73312Xenforo authentication bypass by capture-replay vulnerabilityXenForo before 2.3.13 contains a refresh token replay vulnerability that allows attackers to reuse a refresh token multiple times by exploiting the f…EPSS 0.47%9.1CVE-2026-73309Xenforo vulnerabilityXenForo before 2.3.13 contains an authentication bypass vulnerability in the OAuth2 token endpoint that allows unauthenticated attackers to obtain va…EPSS 0.69%8.8CVE-2024-38457Xenforo cross-site request forgery vulnerabilityXenforo before 2.2.16 allows CSRF.EPSS 7.4%8.8CVE-2024-38458Xenforo code injection vulnerabilityXenforo before 2.2.16 allows code injection.EPSS 0.89%8.7CVE-2026-73314Xenforo vulnerabilityXenForo before 2.3.13 contains a signature verification logic error in the PayPal REST webhook handler that allows unauthenticated attackers to bypas…EPSS 0.65%8.7CVE-2026-73316Xenforo insufficient verification of data authenticity vulnerabilityXenForo before 2.3.13 contains a payment replay vulnerability in the PayPal REST payment provider that allows attackers to process the same webhook p…EPSS 0.27%8.7CVE-2025-71278Xenforo incorrect authorization vulnerabilityXenForo before 2.3.5 allows OAuth2 client applications to request unauthorized scopes. This affects any customer using OAuth2 clients on any version …EPSS 0.27%

Source: NIST National Vulnerability Database (record CVE-2026-73311), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.