bugtraq - Ubuntu, Linux Mint, and the Guest Account

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Date: Sat, 5 May 2012 19:42:00 -0400
From: Jeffrey Walton <noloader@...il.com>
To: FunSec List <funsec@...uxbox.org>,
  Full Disclosure <full-disclosure@...ts.grok.org.uk>,
  BugTraq <bugtraq@...urityfocus.com>
Subject: Ubuntu, Linux Mint, and the Guest Account

I know there's not much new here, but I am amazed that Ubuntu, Linux
Mint and friends ship with a Guest account present and enabled.

The Guest account is surreptitiously added through a lightdm
configuration file, and is not part of the standard user database.
Because its not part of the standard user database, it can't be
disabled through /etc/shadow, nor disable it through familiar tools
such as userdel and usermod. Additionally, the damn account does not
show up in distribution provided tools such as User Accounts applet.

To make matters worse, grepping for guest returns 0 results because
lightdm.conf does not mention one must add the following to disable
the guest account (nothing is required to enable the account):

    allow-guest=false

To add insult to injury, the Guest account is not sandboxed and user
home directories lack sufficient ACLs, so the guest account is able to
wander through user's home directories:

guest-dojMxl@...mint-12-x64 ~ $ pwd
/tmp/guest-dojMxl
guest-dojMxl@...mint-12-x64 ~ $ whoami
guest-dojMxl
guest-dojMxl@...mint-12-x64 /home/jwalton $ cd /home/
guest-dojMxl@...mint-12-x64 /home $ ls -al
total 12
drwxr-xr-x  3 root    root    4096 2012-05-05 16:29 .
drwxr-xr-x 23 root    root    4096 2012-05-05 16:32 ..
drwxr-xr-x  5 jwalton jwalton 4096 2012-05-05 16:35 jwalton
guest-dojMxl@...mint-12-x64 ~ $ cd /home/jwalton/
guest-dojMxl@...mint-12-x64 /home/jwalton $ ls -al
total 28
drwxr-xr-x 5 jwalton jwalton 4096 2012-05-05 16:35 .
drwxr-xr-x 3 root    root    4096 2012-05-05 16:29 ..
-rw-r--r-- 1 jwalton jwalton  220 2012-05-05 16:29 .bash_logout
drwx------ 3 jwalton jwalton 4096 2012-05-05 16:35 .cache
drwxr-xr-x 3 jwalton jwalton 4096 2012-05-05 16:29 .config
drwxr-xr-x 4 jwalton jwalton 4096 2012-05-05 16:29 .mozilla
-rw-r--r-- 1 jwalton jwalton  675 2012-05-05 16:29 .profile
...

 Is there any reason a KIOSK-like account is enabled by default? Do
KIOSKs really dominate the desktop market to warrant the account out
of the box?