Do you not have administrator privileges on your local machine? Do you have Linux and Docker? If the answer to the above questions is yes, then in this article I will show you how to use Docker to modify the sudoers file, allowing you to gain administrator privileges.

Prerequisites

The method presented here requires that the restricted user has access to docker commands, i.e., the user belongs to the docker group. Docker configuration requires the user to belong to this group. This method works only on Linux systems (tested on Ubuntu).

TLDR

• Running alpine linux with the /etc/sudoers file mounted as sudoers in the container:

  docker run -it -v /etc/sudoers:/sudoers --rm alpine /bin/sh

• Changing permissions to edit the sudoers file using vi:

  chmod 777 sudoers
  vi sudoers

• Adding the required permissions to the user in the sudoers file (press i to add an entry):

  # A tab is required between user and ALL (one TAB, not 4 spaces)
  user	ALL=(ALL:ALL) ALL

• Exiting vi with saving:

  :wq

• Changing the permissions of the sudoers file back to default values and exiting the container shell:

  chmod 755 sudoers
  exit

• Verifying changes in the sudoers file:

  cat /etc/sudoers
  sudo su

Description of individual commands

docker run -it -v /etc/sudoers:/sudoers –rm alpine /bin/sh

This command allows you to download the alpine linux image and then run a container from that image. The -it parameter is responsible for running interactive mode (keeps STDIN open even if not attached) and assigning a pseudo-TTY. The -v parameter binds the host’s directory or file to the container’s volume. In this case, we create a binding for the host file /etc/sudoers with the sudoers file in the root directory of our container. The --rm parameter ensures that after closing and exiting the shell, the created container will be removed. The alpine /bin/sh fragment is responsible for selecting the image from which the container will be created (in this case, alpine linux) and running the command (program) /bin/sh, which is the system shell.

chmod 777 sudoers and vi sudoers

The /etc/sudoers file is protected from editing by default. Since alpine is a minimalist linux distribution, it has the vi file editor by default. The sudoers files should be edited using visudo, but alpine does not have this installed by default. To edit the file, you need to grant full permissions to the file for the current user using the chmod 777 sudoers command run in the alpine container. Then you can open the sudoers file using the vi editor with the command: vi sudoers. To be able to enter text in the vi editor, press the i key on the keyboard.

user ALL=(ALL:ALL) ALL

The above entry allows the user to have permissions to execute all commands. The first field indicates the username to which the rule applies (user). The first “ALL” means that this rule applies to all hosts. The second “ALL” means that the user can run commands as all users. The third “ALL” means that the user can run commands as all groups. The fourth “ALL” means that these rules apply to all commands. Remember to maintain the correct formatting in the file. In the case of Ubuntu, there was a tab between user and ALL (not four spaces). Personally, I am not sure if using a single space or 4 spaces will break anything, so to be sure, I kept the target formatting.

Exiting vi

To exit the vi editor saving changes, press the esc key on the keyboard, then type :wq. The commands after the colon are vi commands. w means we want to save the changes made to the file, and q means to close the file.

chmod 755 sudoers and exit

We change the permissions of the sudoers file back to the default values before editing, and then exit the container shell using the exit command. After exiting, the alpine container will be removed. Only the downloaded image will remain on the disk.

cat /etc/sudoers and sudo su

To verify access, we can use the cat /etc/sudoers command to check if the entries were added correctly. We can also use the sudo su command to check if we can execute commands as sudo.

Conclusion

As you can see, docker allows you to change user permissions and modify files that we do not have access to by default. The Docker group belongs to the administrative groups, so a user in this group with access to execute docker commands can modify files without needing administrator access.