PMTUD is not Panacea: Revisiting IP Fragmentation Attacks against TCP

Abstract

There is a widespread belief that TCP is not vulnerable to IP fragmentation attacks since TCP performs the Path Maximum Transmission Unit Discovery (PMTUD) mechanism by default, which can avoid IP fragmentation by dynamically matching the maximum size of TCP segments with the maximum transmission unit (MTU) of the path from the originator to the destination. However, this paper reveals that TCP is in fact vulnerable to IP fragmentation attacks, which is contrary to the common belief.