GHSA-c5c4-8r6x-56w3 OAuth2 Proxy has an Authorization Bypass in Email Domain Validation via Malformed Multi-@ Email Claims

• Go github.com/oauth2-proxy/oauth2-proxy/v7: < 7.15.2 → fixed in 7.15.2

Impact An 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 `[email protected]@company.com` and satisfy an allowed domain check for `company.com`, even though the claim is not a valid email address. The 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. Patches Users should upgrade to `v7.15.2` or later once available. Workarounds The most effective workaround is to ensure the configured identity provider cannot emit malformed or attacker-controlled email claim values.