I would recommend using split to help you out rather than trying to do the whole thing using a regex.

  #  Assuming that the comma delimited stuff is in $_

  my @Values = split ( ",", $_ );
  my $Match = ( $Values[0] eq $Null && 
                $Values[3] eq $Null &&
                $Values[4] eq $Null && 
                $Values[5] eq $Null );
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