External requests initiated by a WordPress server should be considered as security-sensitive. They may contain sensitive data which is stored in the files or in the database of the server. It's important for the administrator of a WordPress server to understand what they contain and to which server they are sent.

WordPress makes it possible to block external requests by setting the `WP_HTTP_BLOCK_EXTERNAL` option to `true`. It's then possible to authorize requests to only a few servers using another option named `WP_ACCESSIBLE_HOSTS`.

== Ask Yourself Whether

* Your WordPress website contains code which may call external requests to servers you don't know.
* Your WordPress website may send sensitive data to other servers.
* Your WordPress website uses a lot of plugins or themes.

There is a risk if you answered yes to any of those questions.


== Recommended Secure Coding Practices

* Uninstall WordPress plugins which send requests to servers you don't know.
* Make sure that `WP_HTTP_BLOCK_EXTERNAL` is defined in `wp-config.php`.
* Make sure that `WP_HTTP_BLOCK_EXTERNAL` is set to `true`.
* Make sure that `WP_ACCESSIBLE_HOSTS` is configured to authorize requests to the servers you trust.

== Sensitive Code Example

----
define( 'WP_HTTP_BLOCK_EXTERNAL', false ); // Sensitive
----


== Compliant Solution

[source,php]
----
define( 'WP_HTTP_BLOCK_EXTERNAL', true );
define( 'WP_ACCESSIBLE_HOSTS', 'api.wordpress.org' );
----

== See

* OWASP - https://owasp.org/Top10/A05_2021-Security_Misconfiguration/[Top 10 2021 Category A5 - Security Misconfiguration]
* OWASP - https://owasp.org/Top10/A10_2021-Server-Side_Request_Forgery_%28SSRF%29/[Top 10 2021 Category A10 - Server-Side Request Forgery (SSRF)]
* https://wordpress.org/support/article/editing-wp-config-php/#block-external-url-requestsl[wordpress.org] - Block External URL Requests
* OWASP - https://owasp.org/www-project-top-ten/2017/A6_2017-Security_Misconfiguration[Top 10 2017 Category A6 - Security Misconfiguration]
* https://owasp.org/www-community/attacks/Server_Side_Request_Forgery[OWASP Attack Category] - Server Side Request Forgery
* CWE - https://cwe.mitre.org/data/definitions/918[CWE-918 - Server-Side Request Forgery (SSRF)]
