For an interesting overview of the unique attack surface presented by Wifi SOCs in general / Broadcom chips in particular as well as a detailed walk through of an interesting vulnerability and how it was used to get code execution on the application processor, check out some recent work by Google Project Zero:

Part 1
https://googleprojectzero.blogspot.com/2017/04/over-air-exploiting-broadcoms-wi-fi_4.html

Part 2
https://googleprojectzero.blogspot.com/2017/04/over-air-exploiting-broadcoms-wi-fi_11.html

As smart phone operating systems present more and more difficult targets to attackers, expect attackers to start looking into other system components as a way in: Cellular baseband, Wifi, bluetooth, NFC, etc. These things are made by third parties and often there is very little known about them, so you can guess that security is not going to be as good. They are ripe grounds for new vulnerabilities and they will only become more attractive to attackers.