Apple’s 10.10.4 OS X update brought a high number of security patches for vulnerabilities reported by the Yahoo Pentest Team. During my research into various OS X frameworks I chose to focus on OS X font parsing and spent a week fuzzing and reversing native libraries. This research resulted in six CVEs, five of which are shared between OS X and iOS.
Client side font parsing is often a good target because the file formats are varied and complicated. For example, TrueType comes with its own turing complete instruction set which you can learn more about here. OTF and the less popular PostScript file formats are complex and also supported.