{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-73309", "assignerOrgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10", "state": "PUBLISHED", "assignerShortName": "VulnCheck", "dateReserved": "2026-08-11T19:56:20.006Z", "datePublished": "2026-09-08T13:15:50.743Z", "dateUpdated": "2026-09-08T13:15:50.743Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10", "shortName": "VulnCheck", "dateUpdated": "2026-09-08T13:15:50.743Z"}, "title": "XenForo < 2.3.13 Authentication Bypass via OAuth2 Token Endpoint", "descriptions": [{"lang": "en", "value": "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."}], "datePublic": "2026-09-07T00:00:00.000Z", "problemTypes": [{"descriptions": [{"lang": "en", "cweId": "CWE-697", "description": "Incorrect Comparison", "type": "CWE"}]}], "affected": [{"defaultStatus": "unaffected", "vendor": "XenForo", "product": "XenForo", "versions": [{"status": "affected", "version": "0", "versionType": "semver", "lessThan": "2.3.13"}]}], "metrics": [{"format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}], "cvssV4_0": {"attackVector": "NETWORK", "attackComplexity": "HIGH", "attackRequirements": "NONE", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "HIGH", "subConfidentialityImpact": "NONE", "vulnIntegrityImpact": "HIGH", "subIntegrityImpact": "NONE", "vulnAvailabilityImpact": "NONE", "subAvailabilityImpact": "NONE", "exploitMaturity": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED", "version": "4.0", "baseSeverity": "CRITICAL", "baseScore": 9.1, "vectorString": "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"}}, {"format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}], "cvssV3_1": {"attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "NONE", "version": "3.1", "baseSeverity": "HIGH", "baseScore": 7.4, "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N"}}], "references": [{"url": "https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/", "name": "Vendor Advisory", "tags": ["vendor-advisory", "patch"]}, {"url": "https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/", "name": "Release Notes", "tags": ["release-notes"]}, {"url": "https://www.vulncheck.com/advisories/xenforo-authentication-bypass-via-oauth2-token-endpoint", "tags": ["third-party-advisory"]}], "credits": [{"lang": "en", "value": "Marco Paciaroni (BomboBombone)", "type": "finder"}, {"lang": "en", "value": "VulnCheck", "type": "coordinator"}], "source": {"discovery": "UNKNOWN"}, "x_generator": {"engine": "vulncheck"}}}}

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{"affected": [{"affectedData": [{"defaultStatus": "unaffected", "product": "XenForo", "vendor": "XenForo", "versions": [{"lessThan": "2.3.13", "status": "affected", "version": "0", "versionType": "semver"}]}], "source": "disclosure@vulncheck.com"}], "cveTags": [], "descriptions": [{"lang": "en", "value": "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."}], "id": "CVE-2026-73309", "lastModified": "2026-09-08T14:17:24.913", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "HIGH", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 7.4, "baseSeverity": "HIGH", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N", "version": "3.1"}, "exploitabilityScore": 2.2, "impactScore": 5.2, "source": "disclosure@vulncheck.com", "type": "Primary"}], "cvssMetricV40": [{"cvssData": {"Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "HIGH", "attackRequirements": "NONE", "attackVector": "NETWORK", "availabilityRequirement": "NOT_DEFINED", "baseScore": 9.1, "baseSeverity": "CRITICAL", "confidentialityRequirement": "NOT_DEFINED", "exploitMaturity": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "privilegesRequired": "NONE", "providerUrgency": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "vectorString": "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", "version": "4.0", "vulnAvailabilityImpact": "NONE", "vulnConfidentialityImpact": "HIGH", "vulnIntegrityImpact": "HIGH", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "source": "disclosure@vulncheck.com", "type": "Secondary"}]}, "published": "2026-09-08T14:17:24.913", "references": [{"source": "disclosure@vulncheck.com", "url": "https://www.vulncheck.com/advisories/xenforo-authentication-bypass-via-oauth2-token-endpoint"}, {"source": "disclosure@vulncheck.com", "url": "https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/"}, {"source": "disclosure@vulncheck.com", "url": "https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/"}], "sourceIdentifier": "disclosure@vulncheck.com", "vulnStatus": "Received", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-697"}], "source": "disclosure@vulncheck.com", "type": "Primary"}]}

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