[MT8.0.x]If PSGI application initialization fails, return 400 Bad Request. MTC-29494

lib/MT/App.pm

@@ -13,6 +13,7 @@ use base qw( MT );
 use File::Spec;
 use MT::Request;
 use MT::Util qw( encode_html encode_url is_valid_email is_url );
+use MT::Util::RequestError qw( parse_init_cgi_error );
 use MT::I18N;
 use MT::Util::Encode;
 
@@ -1141,7 +1142,13 @@ sub init_request {
             }
             require CGI;
             $CGI::POST_MAX = $app->config->CGIMaxUpload;
-            $app->{query} = CGI->new( $app->{no_read_body} ? {} : () );
+            $app->{query} = eval { CGI->new( $app->{no_read_body} ? {} : () ) };
+            if (my $err = $@) {
+                my $res = parse_init_cgi_error($err);
+                $app->{query} = CGI->new( {} );
+                $app->response_code($res->{code});
+                die $res->{message};
+            }
         }
     }
     $app->init_query();

lib/MT/Bootstrap.pm

@@ -278,7 +278,7 @@ sub import {
                     }
                     my $page = $app->show_error(\%param)
                         or die $app->errstr;
-                    print "Content-Type: text/html; charset=$charset\n\n";
+                    $app->send_http_header("text/html; charset=$charset");
                     $app->print_encode($page);
                     exit;
                 };

lib/MT/PSGI.pm

@@ -12,6 +12,7 @@ use parent qw(Plack::Component);
 use Plack::Util::Accessor qw(script application _app);
 use MT;
 use MT::Component;
+use MT::Util::RequestError qw(parse_init_cgi_error);
 use Carp;
 use FindBin;
 use CGI::PSGI;
@@ -55,7 +56,11 @@ my $mt_app = sub {
     return sub {
         my $env = shift;
         eval "require $app_class";
-        my $cgi = CGI::PSGI->new($env);
+        my $cgi = eval { CGI::PSGI->new($env) };
+        if (my $err = $@) {
+            my $res = parse_init_cgi_error($err);
+            return [$res->{code}, [], [$res->{message}]];
+        }
         local *ENV = { %ENV, %$env };    # some MT::App method needs this
         my $app = $app_class->new(CGIObject => $cgi);
         delete $app->{init_request};
@@ -85,7 +90,11 @@ my $mt_app_streaming = sub {
     return sub {
         my $env = shift;
         eval "require $app_class";
-        my $cgi = CGI::PSGI->new($env);
+        my $cgi = eval { CGI::PSGI->new($env) };
+        if (my $err = $@) {
+            my $res = parse_init_cgi_error($err);
+            return [$res->{code}, [], [$res->{message}]];
+        }
         local *ENV = { %ENV, %$env };    # some MT::App method needs this
         my $app = $app_class->new(CGIObject => $cgi);
         delete $app->{init_request};

lib/MT/Util/RequestError.pm

@@ -0,0 +1,52 @@
+# Movable Type (r) (C) Six Apart Ltd. All Rights Reserved.
+# This code cannot be redistributed without permission from www.sixapart.com.
+# For more information, consult your Movable Type license.
+#
+package MT::Util::RequestError;
+
+use strict;
+use warnings;
+use Exporter qw(import);
+
+our @EXPORT_OK = qw(parse_init_cgi_error);
+
+sub parse_init_cgi_error {
+    my ($err) = shift;
+
+    # CGI->new() throws an error if it fails to parse a POST request.
+    # If the boundary is invalid, etc., the error message contains "malformed", so 400 is returned.
+    # In other cases, return 500, most likely due to a bug in the web server or application.
+    # MTC-29494
+    $err =~ m/malformed/i
+        ? {
+        code    => 400,
+        message => "Bad Request: $err",
+        }
+        : {
+        code    => 500,
+        message => 'Internal Server Error',
+        };
+}
+
+1;
+__END__
+
+=head1 NAME
+
+MT::Util::RequestError - Provide utility functions for request error
+
+=head1 METHODS
+
+=head2 parse_init_cgi_error($error)
+
+Parse the error that occurred when `CGI->new` was called.
+Return the response code and message for the error.
+
+Example:
+
+    my $cgi = eval { CGI->new };
+    if (my $error = $@) {
+        my $result = MT::Util::RequestError::parse_init_cgi_error($error);
+        $mt->response_code($result->{code});
+        $mt->print($result->{message});
+    }

t/00-compile.t

@@ -123,6 +123,7 @@ use_ok('MT::FileMgr');
 use_ok('MT::FileMgr::Local');
 use_ok('MT::FileMgr::FTP');
 use_ok('MT::ParamValidator');
+use_ok('MT::Util::RequestError');
 
 # MT7
 use_ok('MT::App::Search::ContentData');