SSL alert number 51 for certain clients

[mstan]

Windows 10
Node v16.16.0

I am attempting to try and run a local MITM proxy for all of my local traffic. I am able to get Windows to look at my locally running instance and most web traffic works fine. However, one client in particular, an Unreal Engine game, throws an error when attempting to establish a connection.

Error: 13424:error:1409441B:SSL routines:ssl3_read_bytes:tlsv1 alert decrypt error:c:\ws\deps\openssl\openssl\ssl\record\rec_layer_s3.c:1546:SSL alert number 51

Some searching on SSL alert number 51 online suggests that either this application isn't supporting a certain cipher, or that the SSL connection is detecting an MITM and preventing it.

I'm not sure how to fix this to make it more permissive. I'm not well educated in this area, but one thing I found online was possibly setting OPENSSL's SECLEVEL to 1, which I'm not sure if handled at this application level or not.

The game works fine using mitmproxy, so this seems specific to node-http-mitm-proxy and not the application itself.

I am not currently attempting any type of traffic manipulation, I'm attempting an unmodified passthrough to-and-from. Other web traffic appears to work without issue.