The vulnerability is that IDToken verifier does not verify if token is properly signed. Signature verification makes sure that the token's payload comes from valid provider, not from someone else. An attacker can provide a compromised token with custom payload. The token will pass the validation on the client side. We recommend upgrading to version 1.33.3 or above

PKCE support is not implemented in accordance with the RFC for OAuth 2.0 for Native Apps. Without the use of PKCE, the authorization code returned by an authorization server is not enough to guarantee that the client that issued the initial authorization request is the one that will be authorized. An attacker is able to obtain the authorization code using a malicious app on the client-side and use it to gain authorization to the protected resource. This affects the package com.google.oauth-client:google-oauth-client before 1.31.0.