Bypassing DEP in Metasploit modules

Data Execution Prevention (DEP) is a protection mechanism that marks certain areas of memory as non-executable, causing no execution of ShellCode when it comes to exploitation. Therefore, even if we are able to overwrite EIP register and point ESP to the start of ShellCode, we will not be able to execute our payloads. This is because DEP prevents the execution of data in the writable areas of the memory such as stack and heap. In this case, we will need to use existing instructions that are in the executable areas to achieve the desired functionality. We can do this by putting all the executable instructions in such an order that jumping to the ShellCode becomes viable.

The technique for bypassing DEP is called Return Oriented Programming (ROP). ROP differs from a normal stack overflow of overwriting EIP and calling the jump to the ShellCode. When DEP is enabled, we cannot do that since the data in the stack is non-executable. Here, instead of jumping...