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Re: TCP SYN packets which have the FIN flag set.



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also sprach Baruch Even <baruch@ev-en.org> [2004.11.05.1229 +0100]:
> This comes from the fact that the NEW state of Netfilter only
> means that this is the first time this connection is seen by the
> firewall. What you really want is the connection to be NEW and
> a valid connection opening, so you check the SYN flag too.

Why do you care about the connection being NEW? I am not
challenging, I just can't figure out an attack scenario that could
exploit the fact that I only check for --syn.

> A former e-mail of mine explains why the --tcp-flags ALL SYN check
> is a bad idea.

You say to use "RST,ACK,FIN,SYN SYN" which makes sense. If you use
--syn and iptables-save, "RST,ACK,SYN SYN" is stored, so this is
what --syn seems to mean. Why does --syn not set FIN in the mask?

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