What is Exploitation

Our general procedure is determined in part by the results of our enumeration and information gathering. We examine the list of known vulnerabilities and potential security holes on the various target hosts and determine which are most likely to be fruitful. Next we pursue exploiting those vulnerabilities to gain root access on the target system.

Primary targets are open ports and potentially vulnerable applications. Our approach is to review the list of vulnerabilities collected in the previous stage and sort them by likelihood of success and potential harm to the target network to see which may be helpful in our exploitation efforts. For instance, a buffer overflow or denial-of-service attack may well be successful on the target but also dangerous to the system. Unless the contract specifically calls for DoS attacks to be performed as part of the test, they should not be attempted.

Among the common exploits performed are Web-server hacks. This is fast becoming a popular way to compromise target networks. One popular Web-based hack is the Microsoft IIS MDAC/RDS hack. This is an exploitation of the IIS Web server through the msadcs.dll file and the Remote Data Service (RDS). It allows the attacker to execute a single command on the target host. The command can be reused to execute a succession of individual commands that when taken together can be used to achieve a variety of results, such as retrieving sensitive files on the target host and making connections to other hosts. Also, when used in conjunction with other tools, such as the ntuser command, it can allow a user to be placed into the local administrator's group.

A Perl script, msdacExploit.pl, coded by rain forest puppy, can remotely exploit this vulnerability and is widely available. (The msdacExploit.pl file is not the only file coded to exploit this hole.) In order to perform this exploit, simply run the following command against the target host.

  C:\> perl –x msdacExploit.pl –h <target host>  

(You do not necessarily have to be in the C drive.) A command prompt from the target host should appear on your machine and allow you to execute one command. To run multiple commands, the exploit must be run multiple times.

Once we have obtained unauthorized access to a remote system through either the ability to execute a command on a target host or direct access to an actual user account, we immediately document all relevant information, including the host and directory or share name to which we have gained access, the host from which we gained access, the date and time, and the level of access. Also, we specify the hole(s) that we exploited to gain access. Next, we share this information with the target organization . This serves two purposes: (1) to alert the organization to the hole(s) we have identified and exploited so that the company can begin to address the issue and (2) to cover ourselves as penetration testers from a litigation standpoint. Even in the case of an unannounced test, our point of contact (who is aware of our activities) should know when we have gained access so if we are detected the matter is not escalated to law enforcement authorities.

Having gained access to one machine is not necessarily the end of our penetration test. If additional work is within scope, we can continue by installing a tool kit comprised of the tools we can use to test other systems from the exploited box. This is different from the “root kit” used within the hacker community to represent a collection of tools and exploits used to either compromise the same system again in the future, by creating back doors or Trojaning system files, or to launch attacks against other hosts, such as distributed denial-of-service daemons.

This tool kit is tailored to the operating system of the target machine and of the machines we may encounter during the penetration test. Generally, we include netcat, password crackers, remote control software, sniffers, and discovery tools. Often, due to the connection, command line tools are preferred. GUI tools can be used if a remote control program such as pcAnywhere or Virtual Network Computing (VNC) is first installed. Otherwise, having the target send a GUI back to our box can be tricky in that it may still be blocked at the firewall or by the host itself. Additionally, it can sometimes display the GUI on the local machine, alerting the machine's user of our presence and activities.

The tool kit can be copied over with FTP or TFTP, but other means are possible as well. Once the kit is installed, we can begin penetration testing other machines. At this point, the methodology we use closely follows the internal testing method since we are essentially located on the target network.

Some of the things we do include are sniffers and keystroke capture utilities through which we can capture client traffic. We are looking specifically for user names and passwords that can be used to attempt access on other hosts, dial-in systems, or listening services on the network.

We also try remote control tools that allow us to control the system. There is tremendous potential for further network compromise once we have taken over one machine. We may capture the UNIX password file (along with the shadow password file) or the Windows registry (often through the version stored in the repair directory) to obtain passwords for all users on the machine and possibly the admin account(s), which likely give us access to additional machines on the network.

In any case, we load whatever tools will help us to use the compromised system as a platform for exploiting additional systems. However, as we load these tools, we keep careful track of what was loaded and where so we can return the system to normal after testing.