Sudo 1.8.14 (RHEL 5/6/7 / Ubuntu) - 'Sudoedit' Unauthorized Privilege Escalation

EDB-ID:

37710


Platform:

Linux

Published:

2015-07-28

# Exploit Title: sudo -e - a.k.a. sudoedit -  unauthorized privilege escalation
# Date: 07-23-2015
# Exploit Author: Daniel Svartman
# Version: Sudo <=1.8.14
# Tested on: RHEL 5/6/7 and Ubuntu (all versions)
# CVE: CVE-2015-5602.

Hello,

I found a security bug in sudo (checked in the latest versions of sudo
running on RHEL and ubuntu) when a user is granted with root access to
modify a particular file that could be located in a subset of directories.

It seems that sudoedit does not check the full path if a wildcard is used
twice (e.g. /home/*/*/file.txt), allowing a malicious user to replace the
file.txt real file with a symbolic link to a different location (e.g.
/etc/shadow).

I was able to perform such redirect and retrieve the data from the
/etc/shadow file.

In order for you to replicate this, you should configure the following line
in your /etc/sudoers file:

<user_to_grant_priv> ALL=(root) NOPASSWD: sudoedit /home/*/*/test.txt

Then, logged as that user, create a subdirectory within its home folder
(e.g. /home/<user_to_grant_priv>/newdir) and later create a symbolic link
inside the new folder named test.txt pointing to /etc/shadow.

When you run sudoedit /home/<user_to_grant_priv>/newdir/test.txt you will
be allowed to access the /etc/shadow even if have not been granted with
such access in the sudoers file.

I checked this against fixed directories and files (not using a wildcard)
and it does work with symbolic links created under the /home folder.