OAuth2 Authorization Code Reuse Vulnerability in XenForo by XenForo Ltd.
CVE-2026-73311

9.1CRITICAL

Key Information:

Vendor

Xen Projectforo

Status
Xen Projectforo
Vendor
CVE Published:
8 September 2026

What is CVE-2026-73311?

XenForo prior to version 2.3.13 is susceptible to a vulnerability that allows an attacker to utilize a previously used OAuth2 authorization code to obtain multiple token pairs. This flaw arises from the system's failure to invalidate authorization codes after their initial use, leading to potential unauthorized access. Attackers can manipulate this oversight to generate independent access tokens for the same user and scopes, undermining the intended single-use mechanism inherent in OAuth2 workflows.

Affected Version(s)

XenForo 0 < 2.3.13

References

https://xenforo.com/community/threads/security-fixes-rele...
vendor-advisorypatch
https://xenforo.com/community/threads/xenforo-2-3-13-and-...
release-notes
https://www.vulncheck.com/advisories/xenforo-oauth2-autho...
third-party-advisory

CVSS V4

Score:
9.1
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
None
Attack Vector:
Network
Attack Complexity:
High
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Marco Paciaroni (BomboBombone)
VulnCheck
.