CVE-2024-2698

A vulnerability was found in FreeIPA in how the initial implementation of
MS-SFU by MIT Kerberos was missing a condition for granting the
“forwardable” flag on S4U2Self tickets. Fixing this mistake required adding
a special case for the check_allowed_to_delegate() function: If the target
service argument is NULL, then it means the KDC is probing for general
constrained delegation rules and not checking a specific S4U2Proxy request.
In FreeIPA 4.11.0, the behavior of ipadb_match_acl() was modified to match
the changes from upstream MIT Kerberos 1.20. However, a mistake resulting
in this mechanism applies in cases where the target service argument is set
AND where it is unset. This results in S4U2Proxy requests being accepted
regardless of whether or not there is a matching service delegation rule.