Changing the jne to je instruction causes program to generate error

Question

I'm trying to change the instruction from jne to je

I've change an instruction

75 0c        jne [some_location]

75 0c is a 2 jump instruction.

So, I've a chaged it to from 75 0c to 74 0c which is also a 2 byte jcc instruction.

The error:

./binary: 1: 00000000:: not found
/* Repeat of the same error but instead of 0000000X where is X is some number */

EDIT: The problem was the hex editor was filtering lines and corrupting data? I was using nvim as the hex edior

Answer 1

You do not need to use an hexadecimal editor with radare2. r2 is a reverse engineering framwork. It does everything.

First ensure radare2 is updated with the latest version:

git clone https://github.com/radareorg/radare2
sh radare2/sys/install.sh

Then open your program in write mode, replace NAMEOFYOURPROGRAM by the name of the program that you want to patch. Then you can overwrite the instruction:

radare2 -a x86 -b 32 -w NAMEOFYOUREXECUTABLE
=> s 0x1343
=> "wa jn 0x1351"

Answer 2

If you want to swap a conditional jump you can use the wao command like this: r2 -qc 'wao recj @ 0x1343' -w YOURPROGRAM.

But you can also use:

• wx 74@0x1343
• wai jne 0x1351@0x1343
• woa 01@!1

(there are many other ways to achieve the same, pick the one you like more)