EUVD Vulnerability Catalog
EUVD-2026-72780
Severity: CRITICAL
Base Score: 9.1
CVSS Version: 4.0
Vulnerability 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.
CVSS Vector Analysis
Below is the complete, human-readable breakdown of the CVSS metric string: 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
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Attack Vector (AV): Network
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Attack Complexity (AC): High
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Attack Requirements (AT): None
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Privileges Required (PR): None
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User Interaction (UI): None
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Vulnerability Confidentiality Impact (VC): High
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Vulnerability Integrity Impact (VI): High
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Vulnerability Availability Impact (VA): None
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Subsequent Confidentiality Impact (SC): None
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Subsequent Integrity Impact (SI): None
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Subsequent Availability Impact (SA): None
Affected Vendors & Systems
Vendor
Xenforo
References & Advisory Links
- https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/
- https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/
- https://bombobombone.github.io/posts/cve-2026-73309/
- https://github.com/BomboBombone/CVE-2026-73309
- https://www.vulncheck.com/advisories/xenforo-authentication-bypass-via-oauth2-token-endpoint
Metadata Profile
Database Authority
European Union Agency for Cybersecurity (ENISA) EUVD
Assigner
VulnCheck
EPSS Probability
0
Known Aliases
CVE-2026-73309
GHSA-pr5w-fh2v-7c9q
Published On
2026-09-08
Last Updated
2026-09-09