When the penetration tester has NOPASSWD privileges to run vi as root, the quickest way to escalate privileges is to leverage vi to execute a shell. The command sudo vi -c ':!bash' opens vi as the root user and immediately spawns a shell within vi. This method is fast and effective because vi (or vim) has the capability to run shell commands.

Executing sudo vi -c ':!bash' will open vi and then immediately run the :!bash command, which spawns a Bash shell with root privileges.

References:

GTFOBins - vi

Example from penetration testing reports where vi is used to escalate privileges: Writeup​​.