Developer Specterdev has published an interesting explanation on the PS4 4.55 exploit, which leverages a race condition in the BPF implementation on FreeBSD.
Interestingly, the writeup mentions that the bug is not PS4 specific, and could be leveraged on other systems running FreeBSD. It seems it was deadlier on the PS4 however, due to how permissions of the dev/bpf device driver are set up in the PS4.
In this exploit, part of the data is being replaced by malicious code, after it has been validated in a different thread (and function) without a mutex lock.
As always, there is no good way to summarize such a writeup without losing most of its useful bits, so head over to SpecterDev’s github to read the full explanation, in particular if you want to understand how hackers find exploits for your favorite console.