{"id":"CVE-2026-40574","aliases":["GHSA-c5c4-8r6x-56w3","BIT-oauth2-proxy-2026-40574","GO-2026-5314"],"title":"OAuth2 Proxy has an Authorization Bypass in Email Domain Validation via Malformed Multi-@ Email Claims","summary":"OAuth2 Proxy has an Authorization Bypass in Email Domain Validation via Malformed Multi-@ Email Claims","severity":"medium","cvss":6.8,"cvssVector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N","vendor":"oauth2-proxy","product":"github.com/oauth2-proxy/oauth2-proxy/v7","ecosystem":"go","affected":["github.com/oauth2-proxy/oauth2-proxy/v7 < 7.15.2"],"patched":["github.com/oauth2-proxy/oauth2-proxy/v7 7.15.2"],"published":"2026-04-15","updated":"2026-07-21","source":"OSV","sourceUrl":"https://osv.dev/vulnerability/GHSA-c5c4-8r6x-56w3","references":[{"url":"https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-c5c4-8r6x-56w3"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-40574"},{"url":"https://github.com/oauth2-proxy/oauth2-proxy"}],"tags":["osv","go"],"epss":0.00209,"epssPercentile":0.113,"ingestedAt":"2026-07-21T19:04:58.697Z","slug":"CVE-2026-40574","body":"## Overview\n\n### Impact\n\nAn authorization bypass exists in OAuth2 Proxy as part of the `email_domain` enforcement option. An attacker may be able to authenticate with an email claim such as `attacker@evil.com@company.com` and satisfy an allowed domain check for `company.com`, even though the claim is not a valid email address.\n\nThe issue **ONLY** affects deployments that rely on `email_domain` restrictions and accept email claim values from identity providers or claim mappings that do not strictly enforce normal email syntax. The practical risk ONLY exists in self-hosted or custom OIDC environments and federated setups where unexpected claim values can reach oauth2-proxy. Standard hosted providers that enforce valid email formatting ARE NOT effected.\n\n### Patches\nUsers should upgrade to `v7.15.2` or later once available.\n\n### Workarounds\nThe most effective workaround is to ensure the configured identity provider cannot emit malformed or attacker-controlled email claim values.\n\n## Affected packages\n\n- `github.com/oauth2-proxy/oauth2-proxy/v7 < 7.15.2`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `github.com/oauth2-proxy/oauth2-proxy/v7 7.15.2`","depth":"sunlit","depthScore":37,"depthScoreParts":{"impact":37.4,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}