As per Dan Moen from Wordfence in the last two weeks, the WordPress.org repository has closed three plugins because they contained content-injection backdoors. “Closing” a plugin means that it is no longer available for download from the repository, and will not show up in WordPress.org search results. Each of them had been purchased in the previous six months as part of the same supply chain attack, with the goal of injecting SEO spam into the sites running the plugins.
What We Know About these Plugins
Duplicate Page and Post
Active Installs: 50,000+
Current Owner: pluginsforwp (joined WordPress.org July 10, 2017)
Sold Date: August 2017
Removed from WordPress.org date: December 14, 2017
The Backdoor Code
This content injection backdoor first appeared in version 4.2.1 (released 4 months ago):
No Follow All External Links
Active Installs: 9,000+
Current Owner: gearpressstudio (joined WordPress.org March 17, 2017)
Sold Date: April 2017
Removed from WordPress.org date: December 19, 2017
The Backdoor Code
This content-injection backdoor first appeared in version 2.1.0 (released 8 months ago).
WP No External Links
The Backdoor Code
This content injection backdoor first appeared in version 4.2.1 (released 4 months ago).
Sold Date: July 12, 2017
Removed from WordPress.org date: December 22, 2017 (we’re assuming this based on the date of the last update note, from a member of the WordPress.org plugins team)
All the above backdoor’s makes a request to cloud-wp.org and will return content based on the URL and user agent passed in the query string. This code runs on every request to the site, so it can be used to inject content to normal site visitors, web crawlers, or the site administrators. We’ve seen content injection in the past, and it’s typically used to inject cloaked backlinks, a form of SEO spam.
Wpconnect.org resolves to the same IP as cloud-wp.org, 188.8.131.52, the API endpoint used in all the three plugin backdoor.
Conclusion and Recommendations
As per Wordfence someone with the name or alias Daley Tias purchased WP No External Links and Duplicate Page and Post. The backdoor code for both plugins call an API endpoint hosted on the same IP. The same company, Orb Online, paid for both the No Follow External Links and Duplicate Page and Posts plugins. Additionally, the purchase solicitation for No Follow All External Links was written from the same template used to solicit the purchase of WP No External Links. All three plugins were purchased by a WordPress.org user that was created within a month of the purchase. Furthermore, the backdoor code used in all three plugins is very similar.
Based on this evidence, it seems that the same criminal actor was responsible purchasing and adding backdoors to all three of these plugins with the goal of injecting SEO spam into the thousands of websites running the plugins. It is not too much of a stretch to assume that Orb Online has been leveraging injected spam links to boost search engine rankings for their customers.
Supply chain attacks targeting WordPress plugins are becoming more and more popular. Wordfence lets you know when a plugin has been removed from the WordPress.org repository. As a site owner, it is incredibly important to stay on top of these, and treat removed (or closed) plugins with an abundance of caution.
If you have any of these plugins running on your site, we recommend that you remove them immediately and that you make sure that SEO spam hasn’t been injected into your site. Even though one of them, WP No External Links, has been updated to remove the backdoor, it has been closed, so it will never be updated again in the future.