The simple_set_acl function in fs/posix_acl.c in the Linux kernel before 4.9.6 preserves the setgid bit during a setxattr call involving a tmpfs filesystem, which allows local users to gain group privileges by leveraging the existence of a setgid program with restrictions on execute permissions. NOTE: this vulnerability exists because of an incomplete fix for CVE-2016-7097.
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