29 Jun

WordPress Plugin Security Review: Google XML Sitemaps

For our twelfth security review of a plugin based on the voting of our customers, we reviewed the plugin Google XML Sitemaps.

If you are not yet a customer of the service you can currently try it free for your first month and then start suggesting and voting on plugins to get security reviews after your first payment for the service. For those already using the service that haven’t already suggested and voted for plugins you can start doing that here.

The review was done on version 4.0.8 of Google XML Sitemaps. We checked for the following issues:

  • Insecure file upload handling (this is the cause of the most exploited type of vulnerability, arbitrary file upload)
  • Deserialization of untrusted data
  • Security issues with functions accessible through WordPress’ AJAX functionality (those are a common source of disclosed vulnerabilities these days)
  • Persistent cross-site scripting (XSS) vulnerabilities in publicly accessible portions of the plugin
  • Cross-site request forgery (CSRF) vulnerabilities in the admin portion of plugins
  • SQL injection vulnerabilities (the code that handles requests to the database)
  • Reflected cross-site scripting (XSS) vulnerabilities
  • Lack of protection against unintended direct access of PHP files
  • Insecure and unwarranted requests to third-party websites


We found several issues, though nothing major, during the review. We notified the developer of the results on June 13, but we have yet to hear back from them and the plugin hasn’t been updated since then.

Before getting into the result we should note that a widely repeated claim that there is a reflected cross-site scripting (XSS) vulnerability in the current version of the plugin is not really true. We were contacted by the person behind the claim back at the beginning March (they also mentioned another claimed vulnerability). After looking into it, we were unable to see how it could be exploited and responded to them asking if they were able to. We never received any response to our query, despite our response coming only 8 hours after they contacted us. The WPScan Vulnerability Database, which usually doesn’t bother to verify vulnerabilities, placed the claim in to their database and from there it has gotten repeated by other providers (usually without disclosing that they are sourcing their information from someone else that hasn’t actual verified the vulnerability). This issue would probably be accurately described as a potential vulnerability and more explanation of why that is can be found here. Several days after it was added to the WPScan Vulnerability Database we started seeing the claim being spread further and we notified the developer of what was going on and they said they would correct the issue, but that has yet to happen.

Broken CSRF Protection

The plugin’s setting page has a section “Recent Support Topics / News” whose results can be enabled/disabled with a link. The link looks like this:


While the URL contains nonce parameter, “_wpnonce”, the underlying code doesn’t check if a nonce is included with a request to enable/disable the results, which leaves it open to cross-site request forgery (CSRF).

Insecure Requests to Developer’s Website

For the first review since we added checking for “Insecure and unwarranted requests to third-party websites” we found a couple of issues. The contents shown as the results in the previously mentioned “Recent Support Topics / News” section of the plugin setting’s page comes from a request to the developer’s website made over HTTP. The setting’s page also includes an iframe showing recent donations that is also loaded over HTTP. The subdomain of the developer’s website where those requests are made to is accessible over HTTPS, making the requests that way would prevent any man in the middle issue with those requests.

Lack of Protection Against Direct Access to Files

Some of the plugin’s .php files lack code at the beginning of the files to restrict direct access to them.  We didn’t see anything that could be exploited in the files without the restriction in place.