The SAML identifier generated within SAML2Utils.java was found to make use of the apache commons-lang3 RandomStringUtils class which makes them predictable due to RandomStringUtils PRNG's algorithm not being cryptographically strong. This issue only affects the 3.X release of pac4j-saml.

If an OpenID Connect provider supports the "none" algorithm (i.e., tokens with no signature), pac4j v5.3.0 (and prior) does not refuse it without an explicit configuration on its side or for the "idtoken" response type which is not secure and violates the OpenID Core Specification. The "none" algorithm does not require any signature verification when validating the ID tokens, which allows the attacker to bypass the token validation by injecting a malformed ID token using "none" as the value of "alg" key in the header with an empty signature value.