The details of exploits used in jailbreaks have typically been released [0] or reverse-engineered [1], so open-source or not, Apple will typically fix them in the subsequent release.

[0] http://conference.hitb.org/hitbsecconf2013ams/materials/D2T1...

[1] http://blog.accuvant.com/bthomasaccuvant/evasi0n-jailbreaks-...