After completing the video lectures of the Security Tube Linux 64 bit Assembler Expert course (SLAE64), a series of assessments must be completed to gain certification. This is the sixth assignment; take three x64 payloads from ShellStorm and create new, polymorphic versions which have the same functionality.

While this sounds super cool, what we’re actually doing is simply changing the content of the shellcode to try to evade detection by basic security tools that use signature based matching to recognise threats. A limitation of the assignment is to stay within 150% of the original payload size.

After completing the video lectures of the Security Tube Linux 64 bit Assembler Expert course (SLAE64), a series of assessments must be completed to gain certification. This is the fifth assignment; analyse 3 payloads generated by the Metasploit msfvenom tool.

msfvenom is a replacement for msfpayload and msfencode tools. It combines their functionality into a single application. The available payloads specifically for x64 Linux are quite limited:

root@kali:~# msfvenom -l | grep linux/x64

linux/x64/exec                                      Execute an arbitrary command
linux/x64/meterpreter/bind_tcp                      Inject the mettle server payload (staged). Listen for a connection
linux/x64/meterpreter/reverse_tcp                   Inject the mettle server payload (staged). Connect back to the attacker
linux/x64/meterpreter_reverse_http                  Run the Meterpreter / Mettle server payload (stageless)
linux/x64/meterpreter_reverse_https                 Run the Meterpreter / Mettle server payload (stageless)
linux/x64/meterpreter_reverse_tcp                   Run the Meterpreter / Mettle server payload (stageless)
linux/x64/shell/bind_tcp                            Spawn a command shell (staged). Listen for a connection
linux/x64/shell/reverse_tcp                         Spawn a command shell (staged). Connect back to the attacker
linux/x64/shell_bind_tcp                            Listen for a connection and spawn a command shell
linux/x64/shell_bind_tcp_random_port                Listen for a connection in a random port and spawn a command shell. 
                                                    Use nmap to discover the open port: 'nmap -sS target -p-'.
linux/x64/shell_find_port                           Spawn a shell on an established connection
linux/x64/shell_reverse_tcp                         Connect back to attacker and spawn a command shell

After completing the video lectures of the Security Tube Linux 64 bit Assembler Expert course (SLAE64), a series of assessments must be completed to gain certification. This is the forth assignment; create a custom encoder/decoder to disguise a shellcode payload.

Many security and threat monitoring tools rely on signature matching to identify bad code. A good way to avoid signature based detection is to obscure the content of a payload with encryption or encoding. The same payload can be repeatedly disguised with different obfuscation schemes. Creating a new encoding method is much simpler than building a new payload.

For the assignment, we will design a simple encoding scheme, create an encoding script to disguise our shellcode and write a decoder stub which we will deploy with the payload to rebuild the original code on the fly.

After completing the video lectures of the Security Tube Linux 64 bit Assembler Expert course (SLAE64), a series of assessments must be completed to gain certification. This is the third assignment; research and create an egg hunter proof of concept.

Egg hunting is a technique which can be used to solve shellcode space restriction problems. The egg hunter is a very small piece of code that searches the process memory for an ‘egg’; a signature consisting of a known sequence of bytes. This signature is used to mark the start of the real payload, which could be much larger. Once the signature is located, the instruction pointer is redirected to the new location and the larger payload is executed.

After completing the video lectures of the Security Tube Linux 64 bit Assembler Expert course (SLAE64), a series of assessments must be completed to gain certification. This write up is for the second assignment: Create a shellcode string that will start a TCP Reverse Shell.

A reverse shell connects to a remote host on a given network address and port. Any commands issued by the remote host are relayed to a local shell on the target in the same way as the bind shell.

Having the target reach out to the remote machine may seem like an odd way of making the connection, especially as the remote must be ready and listening for the connection to be successful. However, this type of connection is preferable if the target is behind a firewall or a network address translation (NAT) layer which would make an inbound connection to a bind shell difficult.

As with the bind shell a passphrase must be implemented to add a layer of security to the program.

After completing the video lectures of the Security Tube Linux 64 bit Assembler Expert course (SLAE64), a series of assessments must be completed to gain certification. The first assignment is to create a shellcode string that will start a TCP Bind Shell.

A bind shell listens on a network port and waits for an incoming connection. When a connection is received, a new socket is created, the I/O streams of the host are cloned into this new socket and a new shell instance is spawned.

This has the effect of giving the remote user an interactive shell on the host system. Of course this is not as secure as something like an SSH connection, but is quite sufficient to let a remote user poke around the host system, issue commands and exfiltrate data.

As an extra twist, the assignment requires a little more security; a passphrase must be implemented in the bind shell code to prevent anyone who happens to stumble across the listening socket from simply dropping into the host shell.

Of course, this ‘security’ is limited and anyone eavesdropping on the connection could sniff the passphrase with minimal effort, but it is an interesting exercise.