How to enter ASCII code "00" and "01" in linux bash?

Question

I have a program that looks like this:

/* buf_overflow.c */ #include <stdio.h> int main(){ char buf[4]; char exploit_buf[4]; fgets(buf, 4, stdin); gets(exploit_buf); printf("exploit_buf: %s\n", exploit_buf); return 0; } 

I am going to use the vulnerability of the get function to overflow the buffer with some other variables. The value I want to write in exploit_buf is AAAAAAAA \ x01 \ x00 \ x00 \ x00, but I don’t know how to send ASCII codes “01” and “00” to exploit_buf.

I know that with this command "printf" AAAAAAAA \ x01 \ x00 \ x00 \ x00 "" you can enter the characters that I want, but I don’t know how to send them to the_buf exploit. I also know that Alt + (the numeric keys to the right of the keyboard) can generate characters from the ASCII code I entered, but this also does not work in my program.

The main problem: "How can I skip the first function" fgets () "and type arbitrary ASCII code into" gets () "?".

Does anyone know how to type arbitrary ASCII code on a Linux command line?

Answer 1

You can use echo -e :

 $ echo -ne 'AAAAAAAA\x01\x00\x00\x00' | python -c 'import sys; print repr(sys.stdin.read())' 'AAAAAAAA\x01\x00\x00\x00' 

-e allows echo interpret escape codes, and -n suppresses the trailing newline.

Note that the Python program displays a string representation of what it received, and that is what we sent using echo .

For more complex exploit strings, it is often easy to use Perl or Python to directly create an exploit string:

 $ perl -e 'print "A" x 1024 . "\0\0\0\1"' | ./buf_overflow 

Answer 2

Enter the following command into the terminal.

 echo $'\000\001' > file1 

This will save the values ​​of ASCII Character 1 and ASCII Character 2 in a file named file1. Now you can read it in your exploit_buf buffer.

Answer 3

Great example from nneonneo.

However, if you want to enter them directly without the help of a script, you can change the configuration of your keyboard to use the "United States (AltGr dead keys)" mode (under "System" → "Settings" → "Keyboard" → "Layout") .), then you can easily use special characters using the right alt button. Examples - é is rAlt + e. ° - rAlt-shift-0-0 (press 0 twice while holding the other buttons).

Answer 4

Since it just inputs the input from standard input, you can simply pass the output of your printf to it:

 printf 'whatever' | myprogram