Hi to all
is possible to use SYNPROXY netfilter module with VyOS ?

Which are the kernel and iptables versions for the latest stable VyOS release?

Any advice?

not out of the box.
You can build customized image which may include this,
but there will be no cli support, and you need to understand internals(you can add anything via post boot script)
iptables v1.4.12.2

CLI support isn’t mandatory. The only missing pieces are kernel and iptables version.
Any change to get that backported from Wheezy in a path release for VyOS ?

Likely it can be tried on 1.2 betas
but I’m pretty sure that it will not happen in 1.1.x