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.
github.com/pac4j/pac4j
github.com/pac4j/pac4j/commit/09684e0de1c4753d22c53b8135d4ef61cfda76f7
github.com/pac4j/pac4j/commit/22b82ffd702a132d9f09da60362fc6264fc281ae
github.com/pac4j/pac4j/commit/9c87bbc536ed5d05f940ae015403120df2935589
nvd.nist.gov/vuln/detail/CVE-2021-44878
openid.net/specs/openid-connect-core-1_0.html#IDToken
www.pac4j.org/4.5.x/docs/release-notes.html
www.pac4j.org/blog/cve_2021_44878_is_this_serious.html