Index: src/wp-includes/user.php
===================================================================
--- src/wp-includes/user.php	(revision 43174)
+++ src/wp-includes/user.php	(working copy)
@@ -3141,8 +3141,36 @@
 	$content = str_replace( '###SITENAME###', wp_specialchars_decode( $email_data['sitename'], ENT_QUOTES ), $content );
 	$content = str_replace( '###SITEURL###', esc_url_raw( $email_data['siteurl'] ), $content );
 
+	$subject = sprintf(
+		/**
+		 * Filters the subject of the email sent when an account action is attempted.
+		 *
+		 * @since 4.9.6
+		 *
+		 * @param string $subject    The email subject.
+		 * @param array  $email_data {
+		 *     Data relating to the account action email.
+		 *
+		 *     @type WP_User_Request $request User request object.
+		 *     @type string          $email       The email address this is being sent to.
+		 *     @type string          $description Description of the action being performed so the user knows what the email is for.
+		 *     @type string          $confirm_url The link to click on to confirm the account action.
+		 *     @type string          $sitename    The site name sending the mail.
+		 *     @type string          $siteurl     The site URL sending the mail.
+		 * }
+		 */
+		apply_filters(
+			'user_request_action_email_subject',
+			/* translators: Privacy data request subject. 1: Site name, 2: Name of the action */
+			__( '[%1$s] Confirm Action: %2$s' ),
+			$email_data
+		),
+		wp_specialchars_decode( get_option( 'blogname' ), ENT_QUOTES ),
+		$email_data['description']
+	);
+
 	/* translators: %s Site name. */
-	return wp_mail( $email_data['email'], sprintf( __( '[%s] Confirm Action' ), wp_specialchars_decode( get_option( 'blogname' ), ENT_QUOTES ) ), $content );
+	return wp_mail( $email_data['email'], $subject, $content );
 }
 
 /**