Differential Fuzzing of Bitcoin implementations

bruno · April 15, 2024, 9:37am

One more bug found by it!

Bug on witness verification (witness flag but empty witnesses)

opened 07:28PM - 12 Apr 24 UTC

By applying differential fuzzing ([bitcoinfuzz](https://github.com/brunoerg/bitc…oinfuzz)) with rust-bitcoin and Bitcoin Core for block deserialization, I found out a bug during the transaction verification step. Basically, it's illegal to have the witness flag present and all witness stacks empty. That is, it has inputs, they have empty witnesses, but the transaction is flagged as segwit. It seems this case is not being catched properly. Base64 to reproduce (for block deserialization): //////////+puampqalJSUlJSUlJSUlJSUlJSUlJSUlJSUlJSUlJSUlJSUlJqampKak4ODg4ODg4qampqVdRqampAgICAgIB/QITAAICAgICAgICAAABAABRAgICAgH9AgICAgICAgICAgICAgICAgICAgICAACRAAIAAAAAAAAAAFECAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgAAApECAAIAAAAAAAAAUQICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAICRAAAAAAAAFv////8AAD0A/////y3/////////AP////8AAQAAAAD///8=