CVE-2021-21291: URL Redirection to Untrusted Site ('Open Redirect')

OAuth2 Proxy is an open-source reverse proxy and static file server that provides authentication using Providers (Google, GitHub, and others) to validate accounts by email, domain or group. In OAuth2 Proxy before version 7.0.0, for users that use the allowlist domain feature, a domain that ended in a similar way to the intended domain could have been allowed as a redirect. For example, if a allowlist domain was configured for “.example.com”, the intention is that subdomains of example.com are allowed. Instead, “example.com” and “badexample.com” could also match. This is fixed in version 7.0.0 onwards. As a workaround, one can disable the allowlist domain feature and run separate OAuth2 Proxy instances for each subdomain.