yii2-authclient is an extension that adds OpenID, OAuth, OAuth2 and OpenId Connect consumers for the Yii framework 2.0. In yii2-authclient prior to version 2.2.15, the Oauth2 PKCE implementation is vulnerable in 2 ways. First, the `authCodeVerifier` should be removed after usage (similar to `authState`). Second, there is a risk for a `downgrade attack` if PKCE is being relied on for CSRF protection. Version 2.2.15 contains a patch for the issue. No known workarounds are available.

Affected: Packagist: yiisoft/yii2-authclient

### Impact _What kind of vulnerability is it? Who is impacted?_

Original Report:

> The Oauth2 PKCE implementation is vulnerable in 2 ways: > 1. The `authCodeVerifier` should be removed after usage (similar to 'authState') > 2. There is a risk for a "downgrade attack" if PKCE is being relied on for CSRF protection.

### Patches _Has the problem been patched? What versions should users upgrade to?_

2.2.15

### Workarounds _Is there a way for users to fix or remediate the vulnerability without upgrading?_

not known yet.

### References _Are there any links users can visit to find out more?_