Authentication bypass via empty OAuth2 credentials
Published Sep 8, 2026 · Updated Sep 9, 2026
Authentication bypass in XenForo before 2.3.13 allows remote attackers to obtain OAuth2 token pairs through the token endpoint. The endpoint checks that client_secret and code_verifier exist but compares them only when their PHP string values are truthy, so empty strings skip both validations. Exploitation still requires a valid authorization code and grants the token scopes approved by the user.
Summary
What happened
Authentication bypass in XenForo before 2.3.13 allows remote attackers to obtain OAuth2 token pairs through the token endpoint. The endpoint checks that client_secret and code_verifier exist but compares them only when their PHP string values are truthy, so empty strings skip both validations. Exploitation still requires a valid authorization code and grants the token scopes approved by the user.
The record
- CVE
- CVE-2026-73309
- Published
- Sep 8, 2026
- Updated
- Sep 9, 2026
- Vendor
- XenForo Ltd.
- Product
- XenForo
- Classifications
- CWE-697, T1550.001
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 8, 2026CVE publishedPublication date reported by the CVE source.
- Sep 9, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0 <2.3.13
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Public exploit references
- CVE-2026-73309 proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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