Yes, AM 8.3 is affected, and there is no patch for 8.3, only upgrade. RSA-2020-03 is written as if the only fix is to update all the way to AM 8.5, but on this discussion...
https://community.rsa.com/message/962123?commentID=962123&et=watches.email.thread#comment-962123
We determined that all of those vulnerabilities addressed in RSA-2020-03 have been remedied within AM 8.4 if you go to Patch 14. There will also be a hot fix for 8.4 P14 addressing the latest Oracle WebLogic vulnerability fixes from the Oracle WebLogic October 2020 CPU and the Oracle WebLogic Nov. 1 2020 hotfix
https://community.rsa.com/docs/DOC-114855
