Active Online Attacks | System Hacking

The easiest way to gain administrator-level access to a system is to guess a simple password assuming the administrator used a simple password. Password guessing is an active online attack. It relies on the human factor involved in password creation and only works on weak passwords.

When we discussed the Enumeration phase of system hacking, you learned the vulnerability of NetBIOS enumeration and null sessions. Assuming that the NetBIOS TCP 139 port is open, the most effective method of breaking into a Windows NT or Windows 2000 system is password guessing. This is done by attempting to connect to an enumerated share (IPC$ or C$) and trying a username and password combination. The most commonly used Administrator account and password combinations are words like Admin, Administrator, Sysadmin, or Password, or a null password.

A hacker may first try to connect to a default Admin$, C$, or C:\Windows share. To connect to the hidden C: drive share, for example, type the following command in the Run field (Start ð Run):

    \\ip_address \c$

Automated programs can quickly generate dictionary files, word lists, or every possible combination of letters, numbers, and special characters and then attempt to log on using those credentials. Most systems prevent this type of attack by setting a maximum number of login attempts on a system before the account is locked.

In the following sections, we'll discuss how hackers can perform automated password guessing more closely, as well as countermeasures to such attacks.

Performing Automated Password Guessing

To speed up the guessing of a password, hackers use automated tools. An easy process for automating password guessing is to use the Windows shell commands based on the standard NET USE syntax. To create a simple automated password-guessing script, perform the following steps:

1. Create a simple username and password file using Windows Notepad. Automated tools such as the Dictionary Generator are available to create this word list. Save the file on the C: drive as credentials.txt.
2. Pipe this file using the FOR command:

     C:\> FOR /F "token=1, 2*" %i in (credentials.txt)
   

3. Type net use \\targetIP\IPC$ %i /u: %j to use the credentials.txt file to attempt to log on to the target system's hidden share.

Note

Another example of how the FOR command can be used by an attacker is to wipe the contents of the hard disk with zeros using the command syntax ((i=0; i<11; i++)); do dd if=/dev/random of=/dev/hda && dd if=/dev/zero of=dev/hda done. The wipe command could also be used to perform the wiping of data from the hard disk using the command $ wipe -fik /dev/hda1.

Defending against Password Guessing

Two options exist to defend against password guessing and password attacks. Both smart cards and biometrics add a layer of security to the insecurity that's inherent when users create their own passwords.

A user can also be authenticated and validated using biometrics. Biometrics use physical characteristics such as fingerprints, hand geometry scans, and retinal scans as credentials to validate users.

Both smart cards and biometrics use two-factor authentication, which requires two forms of identification (such as the actual smart card and a password) when validating a user. By requiring something the user physically has (a smart card, in this instance) and something the user knows (their password), security is increased, and the authentication process isn't susceptible to password attacks.

Note

RSA Secure ID is a two-factor authentication system that utilizes a token and a password.