The KEYS subsystem in the Linux kernel through 4.13.7 mishandles use of add_key for a key that already exists but is uninstantiated, which allows local users to cause a denial of service (NULL pointer dereference and system crash) or possibly have unspecified other impact via a crafted system call.
Exploitability
AV:LAC:LPR:LUI:NScope
S:UImpact
C:NI:NA:H5.5/CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H