oauth2-server (aka node-oauth2-server) through 3.1.1 implements OAuth 2.0 without PKCE. It does not prevent authorization code injection. This is similar to CVE-2020-7692. NOTE: the vendor states 'As RFC7636 is an extension, I think the claim in the Readme of "RFC 6749 compliant" is valid and not misleading and I also therefore wouldn't describe this as a "vulnerability" with the library per se.

Code Injection in oauth2-server