Online wallet platform can be exploited from their vulnerabilities as well and do note that antivirus adds updates on the basis of vulnerabilities known.
What if in the case of unknown vulnerability found by black hat hacker first? Ofc antivirus will not detect such as malware.
Antivirus producer do not update any vulnerabilities (or any databse for vulnerabilities).
They do only update signatures of malicious programs.
A vulnerability in a program/interface/.. is not related to anti virus software in any way.
An AV does recognize malicoius actions on your PC by checking the signature of the executable with their database.
Additionally they analyze the behaviour of such programs (e.g. creating sockets, http requests, ... ).
But this is irrelevant from any vulnerabilities found.