Actually, they released a number of patches all at once, including (quoting
the notice just sent out by firstname.lastname@example.org):
The remainder of the patches (K210-021, K210-022, and U210-025)
add support for IP source checking, and for reducing and/or
eliminating problems associated with SYN attacks, IP fragment
attacks, and some other denial of service/looped server attacks.
Unfortunately, these are available only for BSD/OS 2.1 -- nothing for prior
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