The KEYS subsystem in the Linux kernel before 4.14.6 omitted an access-control check when adding a key to the current task's "default request-key keyring" via the requestkey() system call, allowing a local user to use a sequence of crafted system calls to add keys to a keyring with only Search permission (not Write permission) to that keyring, related to constructgetdestkeyring() in security/keys/request_key.c.