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On 29 November, 2017, WordPress 4.9.1 was released to the public.

Installation/Update Information

To download WordPress 4.9.1, update automatically from the Dashboard > Updates menu in your site's admin area or visit https://wordpress.org/download/release-archive/.

For step-by-step instructions on installing and updating WordPress:

• Updating WordPress

If you are new to WordPress, we recommend that you begin with the following:

• New To WordPress - Where to Start
• First Steps With WordPress or Upgrading WordPress Extended
• WordPress Lessons

Summary

From the WordPress 4.9.1 release post: WordPress versions 4.9 and earlier are affected by four security issues which could potentially be exploited as part of a multi-vector attack. As part of the core team's ongoing commitment to security hardening, the following fixes have been implemented in 4.9.1:

1. Use a properly generated hash for the newbloguser key instead of a determinate substring.
2. Add escaping to the language attributes used on html elements.
3. Ensure the attributes of enclosures are correctly escaped in RSS and Atom feeds.
4. Remove the ability to upload JavaScript files for users who do not have the unfiltered_html capability.

In addition to the security issues above, WordPress 4.9.1 contains 11 bug fixes.

Themes

• #42573 - Templates not working properly
• #42673 - Themes page throws console error when there is only one installed theme

Media

• #42574 - MediaElement upgrade causing JS errors when certain languages are in use e.g de_DE-formal

Rewrite Rules

• #42579 - Correct the logic in extract_from_markers()

Users

• #42242 - `lang` attribute in the admin area doesn't reflect a user's language setting

Text Changes

• #42454 - Unable to translate codex URL in theme-editor.php

Posts

• #42607 - Documentation says "page_attributes_misc_attributes" hook is since 4.8

Editor

• #42609 - Regression: WordPress 4.9 theme editor cannot edit files when running on a Windows based server

Upgrade/Install

• #42628 - New function flatten_dirlist in 4.9 does't play nice with folders with numeric names
• #42641 - On multisite upgrade the wp_blog_versions table doesn't get updated

Database

• #42634 - Regression: Wordpress 4.9 does not parse DB_HOST socket paths with colons correctly

List of Files Revised

wp-admin/about.php
wp-admin/includes/class-wp-upgrader.php
wp-admin/includes/file.php
wp-admin/includes/meta-boxes.php
wp-admin/includes/misc.php
wp-admin/includes/plugin.php
wp-admin/includes/upgrade.php
wp-admin/js/theme.js
wp-admin/js/theme.min.js
wp-admin/theme-editor.php
wp-admin/user-new.php
wp-includes/class-wp-theme.php
wp-includes/feed.php
wp-includes/functions.php
wp-includes/general-template.php
wp-includes/script-loader.php
wp-includes/version.php
wp-includes/wp-db.php