It's not actually that. The jailbreak that we know uses a known PDF exploit to be run. By that, I you do not install "PDF Patcher 2" from Cydia, any website that exploits that PDF bug will have full access to your device (hopefully you will not encounter a malicious site). Apple simply patched that bug in order to prevent your device being controlled by other users. Unfortunately, that patch disables the jailbreak, so it's up to you to update your firmware.
I personally do not see any reasons for updating my device, I jailbroke it using JailbreakMe and then installed PDF Patcher 2 from Cydia, so I'm protected.
Let's say it this way... if you do NOT jailbreak your device (lots of users do not jailbreak theirs) and you open a malicious site, they will be infected. Apple is avoiding that possibility. I don't think it's a direct attack to jailbreakers.
If it has 4.3.3 on it then just use iFaith to obtain that SHSH blob in case a restore is needed.
https://iClarified.com/15394
If it's below 4.3.3 then you're probably put of luck.
How can iOS be vulnerable to the SAME PDF hole?? Wasn't that patched already?
Guess I am missing something which no doubt the tech irobot dudes will inform me...