phpinfo() is a debug functionality that prints out detailed information on both the system and the PHP configuration.

The official PHP documentation makes a recommendation to create a file that calls the phpinfo() function in order to test that the PHP installation was successful; it is a common mistake to forget to remove this file. The information leaked by the phpinfo() function includes physical paths, environment variables, and the full PHP configuration settings.

The phpinfo() is also a debugging tool as it consists of all the information a developer wants to know about a server. If anyone uploads the phpinfo() function to their webroot/index.php file, they can see their server’s configuration settings.

An attacker can obtain information such as:

Exact PHP version.
Exact OS and its version.
Details of the PHP configuration.
PHP compilation options
PHP extensions
Internal IP addresses.
Server environment variables.
Loaded PHP extensions and their configurations.
HTTP headers

This information can help an attacker to gain more information on the system. After gaining detailed information, the attacker can research known vulnerabilities for that system under review. The attacker can also use this information during the exploitation of other vulnerabilities.

Some methods also related to phpinfo