What is hardened PHP?

PHP (Hypertext Preprocessor) is one of the most widely used scripting languages for web development. It offers a user-friendly syntax and can run on various platforms and operating systems. Although PHP is a powerful language, it is also susceptible to security risks and attacks. Attackers can exploit vulnerabilities in the code to gain access to the system, steal data or carry out other malicious activities.

For this reason, it is important that developers harden their PHP applications to minimise potential security risks. This article discusses the fundamentals of PHP hardening, various techniques and best practices for implementation, as well as tools to support hardening. A guide to implementation is also provided. The aim of this article is to help developers make their PHP applications more secure and more resilient to attacks.

Fundamentals of PHP hardening

First familiarise yourself with the basics of PHP and PHP hardening:

What is PHP?

PHP (Hypertext Preprocessor) is a server-side scripting language used to create dynamic web applications. It was created in 1994 by Rasmus Lerdorf and has been continuously developed since then. PHP is used by many well-known websites such as Facebook, Wikipedia and WordPress because it is easy to learn and user-friendly. PHP is also platform-independent and can run on various operating systems such as Windows, Linux and Mac OS.

Why is PHP hardening important?

PHP applications are inherently susceptible to security risks due to the nature of how they are used. Inadequate hardening can allow attackers to exploit programming vulnerabilities to gain access to the system, steal data or carry out other malicious activities. For this reason, it is important that developers harden their PHP applications to minimise potential security risks. PHP hardening encompasses a range of techniques, best practices and tools that can be applied to improve the security of PHP applications.

How does PHP hardening work?

PHP hardening can be achieved through secure configuration of PHP, the use of secure functions, implementation of security checks and the use of encryption. Best practices for PHP hardening include validating user input, avoiding insufficient validation, using parameter binding for database queries and employing secure password storage techniques. Tools for PHP hardening can help identify and remediate vulnerabilities before they can be exploited.

PHP hardening techniques

Here is an overview of the various techniques for PHP hardening:

• Secure configuration options

A secure configuration of PHP can help to minimise potential security risks. This can be achieved by disabling functions and modules that are not required. For example, the functions "eval" and "exec" should be disabled, as they can be used to execute malicious code.

• Use of secure functions

Secure functions should be used to ensure that no malicious input reaches the system. For example, the use of "preg_replace()" should be avoided, as it has a security vulnerability that can allow malicious code to be executed. Instead, "preg_replace_callback()" should be used to prevent malicious input.

• Implementation of security checks

Security checks should be implemented to ensure that user input and data are validated and sanitised before they enter the application. For example, all user input should be validated for validity before it reaches the application. It is also important that all database queries use parameter binding to avoid SQL injection.

• Use of encryption

Encryption should be used to ensure that sensitive data such as passwords and credit card details are transmitted and stored securely. For example, the transmission of data over HTTPS should be used to ensure it is encrypted during transfer. It is also important that passwords are stored securely by being hashed and salted.

Best Practices for PHP Hardening

Find out here which best practices are applied for PHP hardening:

• Validation of user input

All user input should be checked for validity and integrity to ensure it conforms to the expected formats and patterns. This includes inputs such as username, email address, telephone numbers and other information. It is important that all inputs are sanitised to remove unwanted characters before they are processed by the application.

• Avoiding insufficient validation

Insufficient validation can allow malicious code into the system. It is important that all data are checked for validity and integrity before they enter the application. This can be achieved by using regular expressions and other validation techniques.

• Use of parameter binding for database queries

Parameter binding should be used for all database queries to avoid SQL injection. Parameter binding ensures that user input is passed as parameters to the database query rather than being incorporated directly into the query. This prevents malicious code from being injected into the query.

• Use of secure password storage techniques

Passwords should be stored securely by hashing and salting them. It is also important that passwords are stored in the database encrypted or hashed. In addition, passwords should be changed regularly to minimise the risk of compromise. It is also best practice to avoid using passwords with low complexity and length, and to encourage the use of password managers to generate and store strong, secure passwords.

Which tools can be used for PHP hardening?

With the right tools, work in the area of PHP hardening can be made easier:

• PHP scanners

PHP scanners are specialised tools that search for known vulnerabilities in PHP applications. These scanners can automatically review code and identify security flaws before they can be exploited by attackers. Some common PHP scanners are OWASP ZAP, Nikto, Acunetix, Qualys and Nessus.

• PHP security packages

PHP security packages contain specific PHP modules that help to increase the security of PHP applications. These modules provide additional security features such as authentication, encryption, validation, access control and more. Some common PHP security packages are Suhosin, Hardening-Patch, PHPIDS, PHPSecLib and Libsodium.

• PHP code analysis tools

PHP code analysis tools are tools that can be used to review an application's code and uncover vulnerabilities. These tools can automatically search for errors and weaknesses that could potentially be exploited by attackers. Some common PHP code analysis tools are SonarQube, Scrutinizer, PHP_CodeSniffer, PHPStan and PHPMD.

Using tools for PHP hardening can help identify and eliminate potential vulnerabilities in PHP applications before they can be exploited by attackers. However, it is important to note that none of these tools can automatically solve all security issues. A thorough manual review of the application and careful application of best practices for PHP hardening remain essential to ensure the security of PHP applications.

Implementing PHP hardening

Here is a guide to implementing PHP hardening:

Implementing PHP hardening can be a complex task that may vary depending on the type of application. However, here are some general steps that can be followed when implementing PHP hardening:

• Update the PHP version to the latest stable release
• Disable unnecessary PHP modules and functions
• Configure PHP settings for maximum security
• Use secure coding practices when developing applications
• Review the application for known vulnerabilities and security flaws
• Use tools to assess the security of the application and the server

Using frameworks to simplify implementation

Using PHP frameworks can simplify the implementation of PHP hardening, as many of these frameworks provide built-in security features. Some common PHP frameworks known for developing secure applications include Laravel, Symfony, CodeIgniter and CakePHP.

These frameworks provide developers with features such as authentication, validation, encryption and access control. They can also help prevent SQL injection attacks, cross-site scripting (XSS) and other attacks.

However, using a framework for application development does not guarantee a secure application. It is important to continue following PHP hardening best practices and to carry out additional security checks to identify and remediate potential vulnerabilities.

Conclusion

PHP hardening is an important process to ensure that PHP-based applications and servers are secure and protected. Unhardened PHP applications are vulnerable to a variety of attacks such as SQL injection, cross-site scripting and remote code execution.

Overall, it should be noted that PHP hardening is an ongoing process that must be regularly reviewed and updated. Only in this way can you ensure that PHP applications and servers remain protected against new threats. With the right techniques and tools, and continuous review, PHP hardening can be implemented successfully and improve the security of PHP applications and servers.

Our article is based on our own experience and research as well as information from external sources.

Sources & further links on the topic:
http://www.hardened-php.net/ (Website of the Hardened-PHP project)