It was reported  that SSSD improperly expanded group membership when it encountered a non-POSIX group in the group membership chain. For instance:
user -> posix_group1 -> non_posix_group -> posix_group2
With the group memberships noted above, SSSD should include the user as a member of both posix_group1 and posix_group2, however due to the position of the non-POSIX group, SSSD halts processing at it and never reaches posix_group2, leaving the user as a member of posix_group1 and not posix_group2.
SSSD has the capability to set a 'deny' ACL for both users and groups, so in a situation like that illustrated above, if posix_group2 was present in a 'deny' ACL, the user would be granted access because they are not shown as having membership in the denied group. This could grant unintended access to certain users in an environment where non-POSIX groups are used in addition to POSIX groups.
There is currently no patch to correct this issue.
Created sssd tracking bugs for this issue:
Affects: fedora-all [bug 1101756]
This issue affects the version of sssd package as shipped with Red Hat Enterprise Linux 5. The Red Hat Security Response Team has rated this issue as having Low security impact, a future update may address this flaw.
Fixed upstream in version 1.11.7:
This issue was already fixed in sssd updates in Red Hat Enterprise Linux 6 (in 6.6, via RHBA-2014:1375) and Red Hat Enterprise Linux 7 (in 7.1, via RHBA-2015:0441).