passport-wsfed-saml2 provides passport strategy for both WS-fed and SAML2 protocol. A vulnerability present starting in version 3.0.5 up to and including version 4.6.3 allows an attacker to impersonate any user during SAML authentication by crafting a SAMLResponse. This can be done by using a valid SAML object that was signed by the configured IdP. Users are affected specifically when the service provider is using passport-wsfed-saml2 and a valid SAML document signed by the Identity Provider can be obtained. Version 4.6.4 contains a fix for the vulnerability.
When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.