do not apply PSU 12.1.0.1.4 if you are using APEX and the embedded plsql gateway: you might hit bug 18610915 which is internal and therefore no description is available.
if you hit this you are either not able to even bring up the apex login page (neither http nor https) or it stops working after a few connections (dispatchers are dying).
path “Patch 18610915: INTERMITTENT SEGMENTATION FAULT DURING NZ/PRNG INIT” is only available for 12.1.0.2.
Daniel Westermann's Blog 