A "programming error" in fast_ipsec in FreeBSD 4.8-RELEASE through 6.1-STABLE and NetBSD 2 through 3 does not properly update the sequence number associated with a Security Association, which allows packets to pass sequence number checks and allows remote attackers to capture IPSec packets and conduct replay attacks.
https://exchange.xforce.ibmcloud.com/vulnerabilities/25398
http://www.securityfocus.com/bid/17191