A couple weeks ago I wrote a blog post about limiting local Windows administrator rights – the importance of it and some of the things organizations can do to allow end users to work without having those rights (http://bit.ly/1hpyllB). One of the questions that has come up, and it always does, is the question – how bad is it if users have local administrator rights?
Obviously the easiest answer is BAD, REALLY BAD! It’s like you buy a house or a car and then decide that you don’t need locks on any of the doors. The reason we have file permissions, registry permissions, user right assignments, and the like in Windows is to limit ourselves to only having the rights we need on a system that are necessary in order for us to do our jobs. We shouldn’t have any more or any less rights than are necessary. But when we give our end users administrator rights, it is like we’ve just taken all the locks off the doors and given those users the ability to go into any room of the house without our permission.
Ok, so beyond the simple answer, what else could happen on a machine if we allow users to be local administrators of their machines? Here are just a few of the things that could happen:
- System files can be accessed or changed.
- Program files or program configurations could be modified.
- Software that is not approved could be installed, and won’t be maintained.
- Malicious code can be installed with unlimited rights.
- New, unapproved user accounts could be added to the system.
- Password policies could be subverted.
- Security controls such as anti-malware, firewalls, removable media controls, could be disabled.
And as you can imagine, the list goes on and on…
One other fun issue to consider is the issue of passwords. Many people have heard of the pass the hash attack where an attacker steals the local password hash from a machine and then replays it into the system’s memory whenever they want to authenticate as that user. This attack is certainly possible when users have local administrator rights. But wouldn’t it be easier if the user could just steal passwords out of memory in clear text instead? Well it turns out that’s possible too. Enter Mimikatz.
For a nice long, technical explanation of how Mimikatz works, there are plenty of nice tutorials (although to be fair many of them are in French). But here’s the bottom line, if your users are local administrators on their Windows machine, then they will by default have the user right assignment of “Debug Programs” (or they can assign themselves this right if it is taken away by a security policy). Once they have this right they have the ability to interact with sensitive portions of memory, such as those where authentication credentials are stored. With that information they are able to read authentication credentials out of memory as seen in the following screen capture:
Not only are we able to read the NTLM password hash out of memory – which could be taken offline and cracked or used in a pass the hash attach, but we are given the passwords for every logged in user in plain text. Even in the above example where the user is utilizing upper case, lower case, numbers, and special characters and a long password, there is no need for the time or computing resources to crack the password because it is there in clear text.
Many people might wonder at this point, is this only in older versions of Windows? Unfortunately the answer is no. Version 1.0 of Mimikatz works all the way through Windows 8 systems (although Windows 8.1 does appear to be safe). Version 2.0 of Mimikatz works even with Windows 8.1 systems to manipulate this type of information. And if you were wondering, yes, there is integration between Mimikatz and the Metasploit framework to make your penetration testing efforts easier. And, just because, there is also a plugin for Mimikatz for Volatility if you’d like to play with this tool with offline forensic memory dumps.
So once again, let’s restate the issue. How bad is it if end users have local administrator rights on their Windows machines? It’s BAD, REALLY BAD!! Both the Australians DSD in their Top 35 Mitigation Strategies document and the Council on CyberSecurity in their Critical Security Controls document list this issue as a serious concern. Hopefully we can all make sure to keep this issue in mind as we defend our systems.