The filesystem implementation in the Linux kernel through 4.8.2 preserves the setgid bit during a setxattr call, which allows local users to gain group privileges by leveraging the existence of a setgid program with restrictions on execute permissions.
Exploitability
AV:LAC:LPR:LUI:NScope
S:UImpact
C:LI:LA:N4.4/CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N