diff --git a/wp-includes/comment.php b/wp-includes/comment.php
index 635cb59f97..fc423ef2ed 100644
--- a/wp-includes/comment.php
+++ b/wp-includes/comment.php
@@ -1986,6 +1986,15 @@ function wp_update_comment($commentarr) {
 		return 0;
 	}
 
+	$filter_comment = false;
+	if ( ! has_filter( 'pre_comment_content', 'wp_filter_kses' ) ) {
+		$filter_comment = ! user_can( isset( $comment['user_id'] ) ? $comment['user_id'] : 0, 'unfiltered_html' );
+	}
+
+	if ( $filter_comment ) {
+		add_filter( 'pre_comment_content', 'wp_filter_kses' );
+	}
+
 	// Escape data pulled from DB.
 	$comment = wp_slash($comment);
 
@@ -1996,6 +2005,10 @@ function wp_update_comment($commentarr) {
 
 	$commentarr = wp_filter_comment( $commentarr );
 
+	if ( $filter_comment ) {
+		remove_filter( 'pre_comment_content', 'wp_filter_kses' );
+	}
+
 	// Now extract the merged array.
 	$data = wp_unslash( $commentarr );
 
diff --git a/wp-includes/customize/class-wp-customize-header-image-control.php b/wp-includes/customize/class-wp-customize-header-image-control.php
index 8bbb572b8f..471333daec 100644
--- a/wp-includes/customize/class-wp-customize-header-image-control.php
+++ b/wp-includes/customize/class-wp-customize-header-image-control.php
@@ -107,10 +107,10 @@ class WP_Customize_Header_Image_Control extends WP_Customize_Image_Control {
 			<# } #>
 
 			<button type="button" class="choice thumbnail"
-				data-customize-image-value="{{{data.header.url}}}"
+				data-customize-image-value="{{data.header.url}}"
 				data-customize-header-image-data="{{JSON.stringify(data.header)}}">
 				<span class="screen-reader-text"><?php _e( 'Set image' ); ?></span>
-				<img src="{{{data.header.thumbnail_url}}}" alt="{{{data.header.alt_text || data.header.description}}}">
+				<img src="{{data.header.thumbnail_url}}" alt="{{data.header.alt_text || data.header.description}}" />
 			</button>
 
 			<# } #>
diff --git a/wp-includes/customize/class-wp-customize-site-icon-control.php b/wp-includes/customize/class-wp-customize-site-icon-control.php
index 69dea75ed0..a1d655c174 100644
--- a/wp-includes/customize/class-wp-customize-site-icon-control.php
+++ b/wp-includes/customize/class-wp-customize-site-icon-control.php
@@ -70,7 +70,7 @@ class WP_Customize_Site_Icon_Control extends WP_Customize_Cropped_Image_Control
 						<div class="favicon">
 							<img id="preview-favicon" src="{{ data.attachment.sizes.full.url }}" alt="<?php esc_attr_e( 'Preview as a browser icon' ); ?>"/>
 						</div>
-						<span class="browser-title"><?php bloginfo( 'name' ); ?></span>
+						<span class="browser-title"><?php echo esc_js( get_bloginfo( 'name' ) ); ?></span>
 					</div>
 					<img class="app-icon-preview" src="{{ data.attachment.sizes.full.url }}" alt="<?php esc_attr_e( 'Preview as an app icon' ); ?>"/>
 				</div>
diff --git a/wp-includes/date.php b/wp-includes/date.php
index ace3e41bdf..fc425413f3 100644
--- a/wp-includes/date.php
+++ b/wp-includes/date.php
@@ -152,8 +152,8 @@ class WP_Date_Query {
 	 */
 	public function __construct( $date_query, $default_column = 'post_date' ) {
 
-		if ( isset( $date_query['relation'] ) && 'OR' === strtoupper( $date_query['relation'] ) ) {
-			$this->relation = 'OR';
+		if ( isset( $date_query['relation'] ) ) {
+			$this->relation = $this->sanitize_relation( $date_query['relation'] );
 		} else {
 			$this->relation = 'AND';
 		}
@@ -233,6 +233,9 @@ class WP_Date_Query {
 			$this->validate_date_values( $queries );
 		}
 
+		// Sanitize the relation parameter.
+		$queries['relation'] = $this->sanitize_relation( $queries['relation'] );
+
 		foreach ( $queries as $key => $q ) {
 			if ( ! is_array( $q ) || in_array( $key, $this->time_keys, true ) ) {
 				// This is a first-order query. Trust the values and sanitize when building SQL.
@@ -1011,4 +1014,20 @@ class WP_Date_Query {
 
 		return $wpdb->prepare( "DATE_FORMAT( $column, %s ) $compare %f", $format, $time );
 	}
+
+	/**
+	 * Sanitizes a 'relation' operator.
+	 *
+	 * @since 6.0.3
+	 *
+	 * @param string $relation Raw relation key from the query argument.
+	 * @return string Sanitized relation ('AND' or 'OR').
+	 */
+	public function sanitize_relation( $relation ) {
+		if ( 'OR' === strtoupper( $relation ) ) {
+			return 'OR';
+		} else {
+			return 'AND';
+		}
+	}
 }
diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index 7f22a35e5a..4dcfc81cf8 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -2605,8 +2605,16 @@ function wp_nonce_ays( $action ) {
 		$html .= sprintf( __( "Do you really want to <a href='%s'>log out</a>?"), wp_logout_url( $redirect_to ) );
 	} else {
 		$html = __( 'Are you sure you want to do this?' );
-		if ( wp_get_referer() )
-			$html .= "</p><p><a href='" . esc_url( remove_query_arg( 'updated', wp_get_referer() ) ) . "'>" . __( 'Please try again.' ) . "</a>";
+		if ( wp_get_referer() ) {
+			$wp_http_referer = remove_query_arg( 'updated', wp_get_referer() );
+			$wp_http_referer = wp_validate_redirect( esc_url_raw( $wp_http_referer ) );
+			$html           .= '</p><p>';
+			$html           .= sprintf(
+				'<a href="%s">%s</a>',
+				esc_url( $wp_http_referer ),
+				__( 'Please try again.' )
+			);
+		}
 	}
 
 	wp_die( $html, __( 'WordPress Failure Notice' ), 403 );
diff --git a/wp-includes/media-template.php b/wp-includes/media-template.php
index 8d7c758c50..f18688471b 100644
--- a/wp-includes/media-template.php
+++ b/wp-includes/media-template.php
@@ -1245,7 +1245,7 @@ function wp_print_media_templates() {
 			<div class="favicon">
 				<img id="preview-favicon" src="{{ data.url }}" alt="<?php esc_attr_e( 'Preview as a browser icon' ); ?>"/>
 			</div>
-			<span class="browser-title"><?php bloginfo( 'name' ); ?></span>
+			<span class="browser-title"><?php echo esc_js( get_bloginfo( 'name' ) ); ?></span>
 		</div>
 
 		<strong><?php _e( 'As an app icon' ); ?></strong>
diff --git a/wp-includes/pluggable.php b/wp-includes/pluggable.php
index 4c4a32c355..d6dee393bb 100644
--- a/wp-includes/pluggable.php
+++ b/wp-includes/pluggable.php
@@ -305,6 +305,8 @@ function wp_mail( $to, $subject, $message, $headers = '', $attachments = array()
 	$phpmailer->ClearAttachments();
 	$phpmailer->ClearCustomHeaders();
 	$phpmailer->ClearReplyTos();
+	$phpmailer->Body    = '';
+	$phpmailer->AltBody = '';
 
 	// From email and name
 	// If we don't have a name from the input headers
diff --git a/wp-includes/widgets.php b/wp-includes/widgets.php
index 6c559c37e7..940d22b364 100644
--- a/wp-includes/widgets.php
+++ b/wp-includes/widgets.php
@@ -1233,7 +1233,7 @@ function wp_widget_rss_output( $rss, $args = array() ) {
 
 	if ( is_wp_error($rss) ) {
 		if ( is_admin() || current_user_can('manage_options') )
-			echo '<p>' . sprintf( __('<strong>RSS Error</strong>: %s'), $rss->get_error_message() ) . '</p>';
+			echo '<p>' . sprintf( __('<strong>RSS Error</strong>: %s'), esc_html( $rss->get_error_message() ) ) . '</p>';
 		return;
 	}
 
@@ -1342,7 +1342,7 @@ function wp_widget_rss_form( $args, $inputs = null ) {
 	$args['show_date']      = isset( $args['show_date'] ) ? (int) $args['show_date'] : (int) $inputs['show_date'];
 
 	if ( ! empty( $args['error'] ) ) {
-		echo '<p class="widget-error"><strong>' . sprintf( __( 'RSS Error: %s' ), $args['error'] ) . '</strong></p>';
+		echo '<p class="widget-error"><strong>' . sprintf( __( 'RSS Error: %s' ), esc_html( $args['error'] ) ) . '</strong></p>';
 	}
 
 	$esc_number = esc_attr( $args['number'] );
diff --git a/wp-mail.php b/wp-mail.php
index 60287a07bc..4a70c7cc23 100644
--- a/wp-mail.php
+++ b/wp-mail.php
@@ -60,6 +60,9 @@ if( 0 === $count ) {
 	wp_die( __('There doesn&#8217;t seem to be any new mail.') );
 }
 
+// Always run as an unauthenticated user.
+wp_set_current_user( 0 );
+
 for ( $i = 1; $i <= $count; $i++ ) {
 
 	$message = $pop3->get($i);
@@ -125,7 +128,6 @@ for ( $i = 1; $i <= $count; $i++ ) {
 					$author = trim($line);
 				$author = sanitize_email($author);
 				if ( is_email($author) ) {
-					echo '<p>' . sprintf(__('Author is %s'), $author) . '</p>';
 					$userdata = get_user_by('email', $author);
 					if ( ! empty( $userdata ) ) {
 						$post_author = $userdata->ID;
diff --git a/wp-trackback.php b/wp-trackback.php
index 3d211043eb..8fe5b087be 100644
--- a/wp-trackback.php
+++ b/wp-trackback.php
@@ -13,6 +13,9 @@ if (empty($wp)) {
 	wp( array( 'tb' => '1' ) );
 }
 
+// Always run as an unauthenticated user.
+wp_set_current_user( 0 );
+
 /**
  * Response to a trackback.
  *