Manual:$wgAntivirusRequired

Details
Determines if a failed virus scan will cause the file to be rejected. A "failed" scan is one that does not complete successfully for some reason. It does not necessarily mean the file contains a virus (one reason could be that the program does not have enough resources (CPU time, memory)).

If this is set to false, a failed virus scan will be ignored, as if the antivirus feature is disabled.