diff -r 490d5cc509ed -r cf61fcea0001 wp/wp-admin/includes/class-file-upload-upgrader.php
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/wp/wp-admin/includes/class-file-upload-upgrader.php	Mon Oct 14 17:39:30 2019 +0200
@@ -0,0 +1,124 @@
+<?php
+/**
+ * Upgrade API: File_Upload_Upgrader class
+ *
+ * @package WordPress
+ * @subpackage Upgrader
+ * @since 4.6.0
+ */
+
+/**
+ * Core class used for handling file uploads.
+ *
+ * This class handles the upload process and passes it as if it's a local file
+ * to the Upgrade/Installer functions.
+ *
+ * @since 2.8.0
+ * @since 4.6.0 Moved to its own file from wp-admin/includes/class-wp-upgrader.php.
+ */
+class File_Upload_Upgrader {
+
+	/**
+	 * The full path to the file package.
+	 *
+	 * @since 2.8.0
+	 * @var string $package
+	 */
+	public $package;
+
+	/**
+	 * The name of the file.
+	 *
+	 * @since 2.8.0
+	 * @var string $filename
+	 */
+	public $filename;
+
+	/**
+	 * The ID of the attachment post for this file.
+	 *
+	 * @since 3.3.0
+	 * @var int $id
+	 */
+	public $id = 0;
+
+	/**
+	 * Construct the upgrader for a form.
+	 *
+	 * @since 2.8.0
+	 *
+	 * @param string $form      The name of the form the file was uploaded from.
+	 * @param string $urlholder The name of the `GET` parameter that holds the filename.
+	 */
+	public function __construct( $form, $urlholder ) {
+
+		if ( empty($_FILES[$form]['name']) && empty($_GET[$urlholder]) )
+			wp_die(__('Please select a file'));
+
+		//Handle a newly uploaded file, Else assume it's already been uploaded
+		if ( ! empty($_FILES) ) {
+			$overrides = array( 'test_form' => false, 'test_type' => false );
+			$file = wp_handle_upload( $_FILES[$form], $overrides );
+
+			if ( isset( $file['error'] ) )
+				wp_die( $file['error'] );
+
+			$this->filename = $_FILES[$form]['name'];
+			$this->package = $file['file'];
+
+			// Construct the object array
+			$object = array(
+				'post_title' => $this->filename,
+				'post_content' => $file['url'],
+				'post_mime_type' => $file['type'],
+				'guid' => $file['url'],
+				'context' => 'upgrader',
+				'post_status' => 'private'
+			);
+
+			// Save the data.
+			$this->id = wp_insert_attachment( $object, $file['file'] );
+
+			// Schedule a cleanup for 2 hours from now in case of failed installation.
+			wp_schedule_single_event( time() + 2 * HOUR_IN_SECONDS, 'upgrader_scheduled_cleanup', array( $this->id ) );
+
+		} elseif ( is_numeric( $_GET[$urlholder] ) ) {
+			// Numeric Package = previously uploaded file, see above.
+			$this->id = (int) $_GET[$urlholder];
+			$attachment = get_post( $this->id );
+			if ( empty($attachment) )
+				wp_die(__('Please select a file'));
+
+			$this->filename = $attachment->post_title;
+			$this->package = get_attached_file( $attachment->ID );
+		} else {
+			// Else, It's set to something, Back compat for plugins using the old (pre-3.3) File_Uploader handler.
+			if ( ! ( ( $uploads = wp_upload_dir() ) && false === $uploads['error'] ) )
+				wp_die( $uploads['error'] );
+
+			$this->filename = sanitize_file_name( $_GET[ $urlholder ] );
+			$this->package = $uploads['basedir'] . '/' . $this->filename;
+
+			if ( 0 !== strpos( realpath( $this->package ), realpath( $uploads['basedir'] ) ) ) {
+				wp_die( __( 'Please select a file' ) );
+			}
+		}
+	}
+
+	/**
+	 * Delete the attachment/uploaded file.
+	 *
+	 * @since 3.2.2
+	 *
+	 * @return bool Whether the cleanup was successful.
+	 */
+	public function cleanup() {
+		if ( $this->id )
+			wp_delete_attachment( $this->id );
+
+		elseif ( file_exists( $this->package ) )
+			return @unlink( $this->package );
+
+		return true;
+	}
+}