Exploring a public library's computer

When you like looking beyond or using your own tools on computers, it is sometimes infuriating that public computers are limited. Let’s explore one of them.

I am going to go through every try that I did, including failures.

Main restrictions

Pre-Start of this Writeup

MS Office is not installed, so I can’t type a macro that starts Powershell or cmd.

However, Libre Office was instead installed.

I looked through the Internet for an equivalent, but couldn’t find one.

However, I was able to open notepad, and through there create a file at Z:\test.ps1

So I have gone through the apps installed on the computer:

I knew Libre Office couldn’t help me much more than creating a text file. Firefox ang Google Chrome aren’t known for being very helpful in running commands, especially when no access to the settings page is allowed.

I knew that GIMP had an extension system, and that it was based, between others, on Python. So I decided to try. Opening GIMP, going to the menu Filters>Python-Fu. Here, I saw: Console. Opening it, and seeing that it is still python 2.7. Never mind: doing

import os

has opened me PowerShell in almost all it’s glory, except for the environnement: It was still the same as the GIMP’s Python. The main hurtle is the $env:path variable. Getting access to the basic windows softwares is very easy:

$env:path = "C:\Windows\System32;$env:path"

Friday, September 24th 2021

With that I was able to open explorer in the Z:\ folder, and this time with no error messages. Double-clicking on test.ps1, I got a full normal Powershell shell.

Powershell is a very powerfull shell, as its name indicates. Once I got a normal $env:path, I could try to launch diverse Win10 apps, like osk, an on-screen keyboard. It is however less powerfull than his taskbar counterpart, but does the job for a touchscreen acess of the keyboard. I tried to press the Windows+E shortcut on the OSK, but it was again just like I pressed E.

However, the shutdown command was not restricted, even though I couldn't shut the computer:

using the start menu, because it doesn’t exist

pressing alt+f4 on the desktop

using the ctrl+alt+suppr menu, because it is empty.

Which means I tried to logout of my session with

shutdown /l

which had the unintended side effect of showing me the “real” windows 10 login screen.

I then understood that the login system of those computers involve emulating a login screen for the users to type their credentials, and setting up the Z:\ drive to point to this user's personal data.

Which means that everyone is logged as the media user.

After logging back in as the user media with the password media (very creative, by the way), I got the Start menu and button back. But it was still very trimmed down: all the buttons were either empty or errored when clicking on them. Still no right-click.

The login emulator kicked back in, and after entering my credentials, my time limit was reset. So, I had 90 more minutes to try and break the computer.

While I was typing those last words, it was already 6:00 p. m., and the library closed. The computer shut down all by himself, and even my

while (1) {shutdown /a}

wasn’t able to do anything to abort the stop.

If you got there and still have questions, or you just want to give feedback, send an email at albertlarsan@unbon.cafe, and I will add precisions down here.