Wednesday, September 16, 2015

Passing an NTLM Hash to the Browser

In some scenarios, an attacker may have been able to extract Active Directory password hashes but has not been able to successfully crack some or all of them. In this case, it may be possible to perform authentication by merely passing the hash itself, instead of the password. The specific focus of this post, is a pass-the-hash attack on a website which uses NTLM authentication.

(click to zoom)

Under normal circumstances, a user might pull up Internet Explorer and browse to the website which uses NTLM authentication. At that point, if this user is not a domain user, they would typically get a prompt for a username and password. If the user who is logged into the computer is a domain user, they would potentially be automatically logged in using the Windows credentials of the current login session. In the attack, our scenario involves an attacker who has already extracted the victim user's password hash (but not the actual password) and will use it for login. The attacker is logged into Windows with credentials which do not allow them access to the website in question. However, the attacker passes the hash to the current Windows session in order to impersonate the victim user. The attacker then browses to the website using Internet Explorer and is able to automatically authenticate without ever needing the password itself - only the hash. This attack can take place from any computer which is able to access the website. If the website is only accessible internally, as many such NTLM pages are, then the attacker would need to have access to a computer located on the LAN. However, if the website is accessible from the Internet, the attacker could perform the pass-the-hash attack from a remote location outside the network, depending on the individual circumstances. Below are the details on the attack.

Use wce

Extracted hash (extraction process not covered in this post)
Windows computer to perform the attack from
Target website which uses NTLM authentication
Connectivity to the website
wce (Windows Credentials Editor)

wce download link: (expect browser/AV blocking)

Tested on:
Windows 7, 64 bit
Internet Explorer 11, 64 bit
wce v1.4beta x64 (Windows Credentials Editor)


1. Log onto the Windows computer which will be used for the attack
2. Configure Internet Options:
     a. Security>Custom level for the zone>Automatic logon only in intranet zone
     b. Add website to Local Intranet sites
3. Run wce, give it the hash and tell it to call IE: wce -s <UserName>:<DomainName>:<LMHash>:<NTHash> -c "C:\Program Files\Internet Explorer\iexplore.exe"
4. Browse to the website for the automatic login

As you can see, the attack is very simple. Here are the wce command line switches in use:

-s Changes NTLM credentials of current logon session. Parameters: <UserName>:<DomainName>:<LMHash>:<NTHash>.
-c Run <cmd> in a new session with the specified NTLM credentials.

Hmm...Maybe it's time to re-think that Sharepoint NTLM authentication.

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