Always check password to avoid timing side channel attacks on login page

This addresses CVE-2021-38562.

lib/RT/Interface/Web.pm

@@ -804,9 +804,17 @@ sub AttemptPasswordAuthentication {
     my $user_obj = RT::CurrentUser->new();
     $user_obj->Load( $ARGS->{user} );
 
+    # Load the RT system user as well to avoid timing side channel
+    my $system_user = RT::CurrentUser->new();
+    $system_user->Load(1);    # User with ID 1 should always exist!
+
     my $m = $HTML::Mason::Commands::m;
 
     unless ( $user_obj->id && $user_obj->IsPassword( $ARGS->{pass} ) ) {
+        if (!$user_obj->id) {
+            # Avoid timing side channel... always run IsPassword
+            $system_user->IsPassword( $ARGS->{pass} );
+        }
         $RT::Logger->error("FAILED LOGIN for @{[$ARGS->{user}]} from $ENV{'REMOTE_ADDR'}");
         $m->callback( %$ARGS, CallbackName => 'FailedLogin', CallbackPage => '/autohandler' );
         return (0, HTML::Mason::Commands::loc('Your username or password is incorrect'));

lib/RT/User.pm

@@ -976,15 +976,18 @@ sub IsPassword {
     }
 
    if ( $self->PrincipalObj->Disabled ) {
+        # Run the bcrypt generator to avoid timing side-channel attacks
+        RT::Util::constant_time_eq($self->_GeneratePassword_bcrypt($value), '0' x 64);
         $RT::Logger->info(
             "Disabled user " . $self->Name . " tried to log in" );
         return (undef);
     }
 
     unless ($self->HasPassword) {
-        return(undef);
-     }
-
+        # Run the bcrypt generator to avoid timing side-channel attacks
+        RT::Util::constant_time_eq($self->_GeneratePassword_bcrypt($value), '0' x 64);
+        return undef;
+    }
     my $stored = $self->__Value('Password');
     if ($stored =~ /^!/) {
         # If it's a new-style (>= RT 4.0) password, it starts with a '!'