As announced on reddit and discussed on twitter, a problem in TaiG jailbreak might allow any app to be root.
TaiG jailbreak seems to have a broken setreuid() that allows root privilege escalation.
There is no much to say right now, but definitely you should be more careful when installing cydia tweaks from random people / repos.
Saurik, creator of Cydia said:
I already talked to TaiG about this awkward kernel patch days ago, and have this on my schedule of things to fix “next” (after the thing I’m working on fixing right now).
We will definitely keep you update on this subject as soon as we find out more!