Metasploit Revealed: Secrets of the Expert Pentester

Using NASM shell for writing assembly instructions

Metasploit provides a great utility for writing short assembly codes using the NASM shell. The generate_seh_record() method created an SEH frame automatically and used a small assembly code in the previous section; \xeb\x0a, which denoted a short jump of 12 bytes. However, in case of generation of a manual SEH record, instead of searching the internet for op codes, we can use the NASM shell to write assembly codes with ease.

In the previous example, we had a simple assembly call, which was JMP SHORT 12. However, we did not know what op-codes match this instruction. Therefore, let's use NASM shell and find out as follows:

We can see in the preceding screenshot that we launched nasm_shell.rb ...