Are P2PKH or P2SH transactions malleable? BIP66 fixed one source of transaction malleability and segwit, to my understanding, fixed the rest of the sources. Yet, there are still many common types of non-segwit transactions in use, like P2PKH P2SH(PWPKH) P2SH-multisig, are these subject to malleability attacks by a stranger?
I understand that even if someone knows how to do a malleability attack on these transactions, he might choose to answer &quot;no&quot; (or don't answer) to prevent these attacks. But, on the other hand, if a malleability attack on these common transactions was possible, I believe someone that wants to push for segwit adoption would have already build an app to systematically attack.
Yes. Many of the malleability sources listed in BIP 62 still exist today. Most (if not all) are not standard, i.e. most nodes will not relay transactions that exploit them, but they are not consensus rules. So a miner can still perform malleability attacks.