A SAML library not dependent on any frameworks that runs in Node. In version 5.0.1, Node-SAML loads the assertion from the (unsigned) original response document. This is different than the parts that are verified when checking signature. This allows an attacker to modify authentication details within a valid SAML assertion. For example, in one attack it is possible to remove any character from the SAML assertion username. To conduct the attack an attacker would need a validly signed document from the identity provider (IdP). This is fixed in version 5.1.0.
When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.