Insecure Functions in PHP Applications and How to Mitigate Them

PHP Attack Example

While PHP itself isn’t inherently insecure, many of its functions do not adequately validate and sanitize user input. This can leave applications open to vulnerabilities like SQL injection, code execution, and path traversal.

A CSRF attack exploits the fact that web pages send a session ID in a cookie and allows attackers to impersonate the victim and perform unauthorized actions. To mitigate this, use a nonce to verify every request.

Buffer Overflow

This vulnerability happens when a program tries to store more data in a buffer than it can hold. This can lead to a program crash or to malicious code being executed. It is one of the most common vulnerabilities found in PHP applications.

This type of attack exploits a bug in the way that a web application handles user input. PHP applications often use functions like eval() or phpInfo() that take user input and execute it. If these functions do not properly validate and sanitize user input, they can introduce serious vulnerabilities into the application.

These vulnerabilities can expose routes that should not be accessible, or they can interfere with the backend operations of a web application. This could allow attackers to manipulate the content of the website or even to perform a Denial Of Service on resource intensive operations. This is one of the reasons why it is important to always keep your web application up to date with security patches.

Object Injection

Object injection is one of the more complex types of vulnerabilities. It occurs when a web application uses a function that takes un-sanitized user input and then injects PHP objects into memory. These objects implement PHP magic methods such as _destruct, _construct and _wakeup and the attacker can use these class variables to carry out a range of attacks.

To understand the vulnerability it is helpful to review how serialization and deserialization works in a programming language. Serialization is the process of converting an object into a format that can be stored or transferred and deserialization is the reverse, turning a stored object back into a PHP object.

Insecure deserialization vulnerabilities (or Object Injection in this case) occur when developers recklessly use functions such as include(), include_once(), fopen(), file_get_contents() and require_once() to load PHP code or content from a malicious source. This can be abused to bypass authentication, execute arbitrary commands or access data that is normally protected from remote HTTP requests.

SQL Injection

SQL injection is a common vulnerability in web applications. It allows hackers to steal user data and disrupt a website’s operations. It typically occurs when a website has poor input sanitization in a form or comment section.

This vulnerability occurs when developers use untrusted input to load PHP code or content. It can be carried out using functions like include, include_once, fopen, file_get_contents, and require_once.

Attackers can perform path traversal by injecting new path elements in the URL to backtrack up to parent directories that are otherwise hidden from users. This way, they can access files that are outside the /public directory that is accessible from the web application’s server. They can also manipulate classes whose constructors perform tasks that could cause problems in the backend. This can lead to a denial of service. It can also lead to data manipulation or a compromise of an administrator account. This is a serious concern for a lot of websites that need to store data in databases.

Remote Code Execution (RCE)

RCE vulnerabilities are the result of bugs in a web application that allow an attacker to upload and execute code. The attacks are a serious threat because they usually give an attacker full access to your website immediately after being exploited.

PHP functions like eval(), include, require_once, fopen and file_get_contents allow an attacker to load a local file that contains PHP code or content and run it on the vulnerable website. These attacks can be combined with other vulnerabilities like SQL Injection and Path Traversal to enable various kinds of attacks.

When dealing with user inputs in a web application it is essential to properly validate and sanitize the data. This includes checking if the data is the kind you need, verifying it has the proper format and removing illegal characters. Invalidating and sanitizing are the first steps in keeping your website safe from a wide range of threats. It’s also important to use a vulnerability scanner to monitor for these types of vulnerabilities.

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