Quay: ldap referral filter injection in quay external ldap authentication

A flaw was found in Red Hat Quay's external Lightweight Directory Access Protocol (LDAP) authentication handling. When an LDAP referral is returned during authentication, the system does not properly escape the username input. This allows an attacker to inject LDAP filter metacharacters, enabling user-existence oracle attacks at the referral Directory Name (DN). This could also potentially influence which DN is used for password binding in multi-domain Active Directory environments.