** DISPUTED ** kernel/ptrace.c in the Linux kernel through 4.4.1 mishandles uid and gid mappings, which allows local users to gain privileges by establishing a user namespace, waiting for a root process to enter that namespace with an unsafe uid or gid, and then using the ptrace system call. NOTE: the vendor states "there is no kernel bug here."
Debian Linux Security Advisory 3434-1 - Several vulnerabilities have been discovered in the Linux kernel that may lead to a privilege escalation, denial of service or information leak.