The (1) IPv4 and (2) IPv6 implementations in the Linux kernel before 3.1 use a modified MD4 algorithm to generate sequence numbers and Fragment Identification values, which makes it easier for remote attackers to cause a denial of service (disrupted networking) or hijack network sessions by predicting these values and sending crafted packets.
https://support.f5.com/csp/article/K15301?utm_source=f5support&%3Butm_medium=RSS
https://github.com/torvalds/linux/commit/bc0b96b54a21246e377122d54569eef71cec535f
https://github.com/torvalds/linux/commit/6e5714eaf77d79ae1c8b47e3e040ff5411b717ec
https://bugzilla.redhat.com/show_bug.cgi?id=732658
http://www.openwall.com/lists/oss-security/2011/08/23/2
http://www.kernel.org/pub/linux/kernel/v3.x/ChangeLog-3.1