CODEWITHSUNDEEP
cbash
Afshin
Afshin

Reputation: 439

Why is my setenv() call not working?

I wrote the following C code to set the env variable to \x09. But when I use echo $EGG | hexdump, I see that it sets it to 00. This problem happens only when the first nibble is zero. Any clue what is wrong?

char shellcode[] = "\x09";

main() {
    setenv("EGG", shellcode, 1);
    system("/bin/bash");

    return 0;
}

Upvotes: 4

Views: 517

Answers (2)

Dmytro Sirenko
Dmytro Sirenko

Reputation: 5083

The problem is that characters 0x08, 0x09, 0x0a, 0x0b, 0x0c ... are considered whitespace characters and are stripped from a variable value. If you try to set 0x01, it'll be visible in the shell.

P.S. It looks like the variable is set to \x09 but is not echoed by the shell: Indeed:

prev_sh_$ ./so2 
$ export IFS=" \n"
$ echo $EGG | hexdump
0000000 0a09                                   
0000002

0x0a (\n) is added by the shell to print the value on the next line.

Upvotes: 4

P.P
P.P

Reputation: 121417

Well, your code works correctly ;)

0x09 is the ASCII code tab key.

So EGG is set to tab key. When you print it, it actually prints tab which you don't normally recognize in the console.

Upvotes: 2

Related Questions