EUVD-2026-72780
GHSA-pr5w-fh2v-7c9q
Severity by source
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:X/V:X/RE:X/U:X
Network, unauthenticated, but requires possessing a valid authorization code (AC:H); token issuance yields high confidentiality and integrity impact with no availability effect.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
Lifecycle Timeline
3DescriptionCVE.org
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.
Articles & Coverage 2
AnalysisAI
Authentication bypass in XenForo before 2.3.13 lets unauthenticated attackers redeem a valid OAuth2 authorization code for a real access/refresh token pair by submitting empty client_secret and code_verifier values at the token endpoint. Because PHP treats empty strings as falsy, both client-secret verification and PKCE code-verifier checks are silently skipped, defeating client authentication and the PKCE binding. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires XenForo's OAuth2 authorization server to be in use and its token endpoint reachable, plus the attacker must possess a valid, unexpired authorization code issued for a target client (typically a confidential client using a secret and/or a public client using PKCE). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The supplied CVSS 4.0 vector (AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N) scores 9.1 and is internally consistent: network-reachable, unauthenticated, high confidentiality and integrity impact, no availability impact. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Vendor-released patch: upgrade to XenForo 2.3.13, or apply the corresponding backported security release on the 2.2.x line as described at https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/ and https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, audit your environment to identify all XenForo instances and document their current versions to confirm exposure scope. …
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Same weakness CWE-697 – Incorrect Comparison
View allSame technique Authentication Bypass
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External POC / Exploit Code
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