OP_CHECKSIG signature hash type 0
I've done some testing with pybitcointools and one of the BitcoinCore test vectors with a SIGHASH of zero.

For SIGHASH =0, the Tx which is signed 

It's just a matter of appending 4 nullbytes, instead of 01000000, to the signing transaction. 

The Core software checks for this non-standard hashtype now, however we can see there's no problem in validating these rare transactions since the code only checks for SIGHASH ACP, SINGLE &amp; NONE. See Python-Bitcoinlib's code for a Python interpretation

See this test vector, where the hash being validated is 11743b220e9e24e89abd4ff124a2740531fe7d7f9b4e26de14710a532fd543e2.

FWIW, Pybitcointools needs to have the txhash function edited so that instead of if hashcode:, it reads if hashcode is not None:. The else clause in that function was confusing me, but it appears to be for hashing signed transactions (ie to return the TxID)