SHA-2 is an open algorithm and it uses as its constants the sequential prime cube roots as a form of "nothing up my sleeve numbers". For someone to find a weakness or backdoor in SHA would be the equivalent of the nobel prize in cryptography. Everyone who is anyone in the cryptography community has looked at SHA-2. Not just everyone with a higher degree in mathematics, computer science, or cryptography in the last 20 years but foreign intelligence agencies and major financial institutions. Nobody has found a flaw, not even an theoretical one (a faster than brute force solution which requires so much energy/time as to be have no real world value).
To believe the the NSA has broken SHA-2 would be to believe that the NSA found something the entire rest of the world combined hasn't found for twenty years. Also NIST still considers SHA-2 secure and prohibits the use of any other hashing algorithm (to include SHA-3 so far) in classified networks. So that would mean the NSA is keeping a flaw/exploit from NIST compromising US national security.
Anything is possible but occam's razor and all that.
Correct me if I'm wrong and misread sometime off one of news sites, but I understood that the NSA was able to intercept, then index all transmissions prior to the encryption process. To me, this made perfect sense when I read it, for then it wouldn't matter what SHA(?) is used, the information would already be mirrored and stored, somehow allowing the NSA to act as the man-in-the-middle.