Multiple TCP implementations with Protection Against Wrapped Sequence Numbers (PAWS) with the timestamps option enabled allow remote attackers to cause a denial of service (connection loss) via a spoofed packet with a large timer value, which causes the host to discard later packets because they appear to be too old.
The TCP/IP stack in multiple operating systems allows remote attackers to cause a denial of service (CPU consumption) via a TCP packet with the correct sequence number but the wrong Acknowledgement number, which generates a large number of "keep alive" packets. NOTE: some followups indicate that this issue could not be replicated.