A certain pseudo-random number generator (PRNG) algorithm that uses XOR and 2-bit random hops (aka "Algorithm X2"), as used in OpenBSD 2.6 through 3.4, Mac OS X 10 through 10.5.1, FreeBSD 4.4 through 7.0, and DragonFlyBSD 1.0 through 1.10.1, allows remote attackers to guess sensitive values such as IP fragmentation IDs by observing a sequence of previously generated values. NOTE: this issue can be leveraged for attacks such as injection into TCP packets and OS fingerprinting.
https://exchange.xforce.ibmcloud.com/vulnerabilities/41155
https://exchange.xforce.ibmcloud.com/vulnerabilities/40329
http://www.securityfocus.com/bid/27647
http://www.securityfocus.com/archive/1/487658
http://www.securiteam.com/securityreviews/5PP0H0UNGW.html
http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/netinet/ip_id.c?rev=1.10%3Bcontenttype=
http://secunia.com/advisories/28819