PHP Security-Remote File Risk

Remote file risk

PHP has a configuration option called allow_url_fopen, which is enabled by default. It allows you to point to many types of resources and treat them like local files. For example, you can get the content (HTML) of a page by reading the URL:

As discussed in Chapter 5, serious vulnerabilities can arise when tainted data is used to point to files in include and require. In fact, I consider this vulnerability to be one of the most dangerous in PHP applications because it allows an attacker to execute arbitrary code.

Although slightly less severe, a similar vulnerability can result from using tainted data in a standard file system function:

## This example enables the user to manipulate file_get_contents( ) behavior so that it obtains the contents of the remote resource. Consider a request similar to the following:

http://www.php.cn/ ... mple.org%2Fxss.html

This leads to a situation where the value of $content is tainted. Since this value is obtained indirectly, this fact is likely to be ignored. This is why the defense-in-depth principle treats the file system as a remote data source and the value of $content as input, so your filtering mechanism can potentially turn things around.

Because the $content value is contaminated , it can lead to a variety of security vulnerabilities, including cross-site scripting vulnerabilities and SQL injection vulnerabilities. For example, here is an example of a cross-site scripting vulnerability:

## The above process provides a powerful method to prevent various attacks, and is recommended for use in actual programming.

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