I may be blind but I just can't see what the iptables latest version is.
I've checked iptables homepage.
I've also searched the internet and nothing.
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As far as I can read, latest version is 1.4.21 from Nov 22nd 2014. Link
iptable releases are here: https://www.netfilter.org/projects/iptables/downloads.html
At time of writing, the latest is iptables-1.6.2, but it updates pretty often.