A vulnerability that lurked in the Linux kernel for 19 years allows low-privileged users to obtain root-level privileges on numerous distributions. Dubbed CIFSwitch, the issue impacts the Linux kernel’s CIFS subsystem and the cifs-utils userspace helper it uses for handling authentication. CIFS handles parts of the SMB network filesystem protocol, such as mounting shares, read/write actions, and SMB communication to the server. When authenticating a mount, the subsystem sends a request_key call for a cifs.spnego key. The request checks the key in userspace and calls cifs.upcall as root to parse the key description, which contains fields such as UID, PID, credential cache, and namespace. According to SpaceX security engineer Asim Viladi Oglu Manizada, the kernel does not check the origin…