CVE-2021-39191

mod_auth_openidc is an authentication/authorization module for the Apache
2.x HTTP server that functions as an OpenID Connect Relying Party,
authenticating users against an OpenID Connect Provider. In versions prior
to 2.4.9.4, the 3rd-party init SSO functionality of mod_auth_openidc was
reported to be vulnerable to an open redirect attack by supplying a crafted
URL in the target_link_uri parameter. A patch in version 2.4.9.4 made it
so that the OIDCRedirectURLsAllowed setting must be applied to the
target_link_uri parameter. There are no known workarounds aside from
upgrading to a patched version.