Why Should These Issues Be Considered Important?
WordPress recommends installing this update as soon as possible due to the severity of the issues that it resolves. It isn’t immediately clear but 24 security issues were addressed in this update. Please find below a summary of those issues:
- A redirect bypass in the customizer (which could be used by an attacker to redirect to websites to perform attacks such as watering hole attacks (defined))
- 2x cross site scripting (XSS) vulnerabilities (defined) as a result of attachment names
- Revision history information disclosure
- A denial of service issue (defined)
- some less secure sanitize_file_name edge cases
- unauthorized category removal from a post
- password change via stolen cookie (defined)
Previously in early May this year WordPress made available version 4.5.2. This was also an important security update that addressed 2 security vulnerabilities. The first relates to a Same Origin Method Execution (SOME) (defined) vulnerability. This vulnerability is similar to a cross site scripting (XSS) vulnerability since it abuses JSON (defined) callbacks.
The second issue addressed is a more traditional cross site scripting (XSS) vulnerability within a 3rd party library, namely MediaElement.js.
Separately in early June WordPress removed a plugin named WP Mobile Detector from their plugin website when attacks begin exploiting a trivially exploitable zero-day vulnerability (defined) within it.
Researchers at the security firm Sucuri were able to determine that the attacks for this vulnerability began on the 27th of May. The vulnerability was then disclosed on the Plugin Vulnerabilities website. The vulnerability allows an attacker to upload a file of their choice to a WordPress website.
Finally, and as above in late May the security firm Sucuri discovered a critical (due to the ease of exploitation) cross site scripting (XSS) vulnerability in the popular WordPress Jetpack plugin. This issue affected more than 1 million WordPress websites.
How Can I Protect Myself from These Issues?
As always; WordPress users can update their CMS manually (access your WordPress dashboard and choose Updates -> Update Now). Since version 3.7 of WordPress an automatic updater (thanks to Sophos for this useful piece of information) will install the above mentioned update in the background. WordPress.com hosted blogs such as the one you are reading now automatically receive such security updates.
For the WP Mobile Detector; it was later updated to version 3.6 to address this vulnerability. However as noted by Sucuri in their advisory the vulnerability was not fully addressed by this new version and they are working with them to address this further shortcoming.
If you use the WP Mobile Detector plugin, please ensure that you are using the most recent version. While the vulnerability is difficult to exploit since it requires the allow_url_fopen API (defined) to be enabled. US CERT recommends disabling this API (defined) call if it is not needed for your website as a defence in depth (defined)(PDF) measure.
Lastly for the JetPack plugin, please update to version 4.0.3 or later to resolve the above mentioned critical XSS issue. Updates were also made available for all 21 code branches of the plugin if you are not already using the newest code branch. The developers of the plugin have also provided an FAQ for this update as well as the steps to install it.