What is hardened PHP?

PHP (Hypertext Preprocessor) is one of the most commonly 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 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. This article discusses the fundamentals of PHP hardening, various techniques and best practices for implementation, and tools to support hardening. An implementation guide is also provided. The aim of this article is to help developers make their PHP applications more secure and resilient against attacks.

Fundamentals of PHP hardening

Familiarise yourself first 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 developed by Rasmus Lerdorf in 1994 and has been continuously developed ever since. 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, by their nature of use, susceptible to security risks. Inadequate protection 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 comprises 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 safe 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 in database queries and employing secure password storage techniques. PHP hardening tools can help identify and remediate vulnerabilities before they can be exploited.

Techniques for PHP hardening

Here you will find an overview of the different techniques in the area of PHP hardening:

• Secure configuration options

A secure configuration of PHP can help minimise potential security risks. This can be achieved by disabling unnecessary functions and modules. For example, the functions "eval" and "exec" should be disabled, as they can be used to execute malicious code.

• Use of safe functions

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

• Implementation of security checks

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

• Use of encryption

Encryption should be used to ensure that sensitive data such as passwords and credit card information are transmitted and stored securely. For example, data transmission should occur over HTTPS to ensure it is encrypted during transmission. 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 to PHP hardening:

• Validation of user input

All user input should be checked for validity and integrity to ensure it matches the expected formats and patterns. This includes inputs such as username, e-mail 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 to enter the system. It is important that all data be checked for validity and integrity before it enters the application. This can be achieved by using regular expressions and other validation techniques.

• Use of parameter binding in database queries

Parameter binding should be used in all database queries to avoid SQL injections. 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 being hashed and salted. It is also important that passwords in the database are stored encrypted or hashed. Additionally, passwords should be changed regularly to minimise the risk of compromise. It is also best practice to avoid using short or low-complexity passwords 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 hardened PHP 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 detect security issues 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 include specialised PHP modules that help 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 inspect an application's code and expose vulnerabilities. These tools can automatically look 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 resolve 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.

Implementation of PHP hardening

Here you will find a guide to implementing PHP hardening:

Implementing PHP hardening can be a complex task that varies 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 make implementing PHP hardening easier, as many of these frameworks provide specific 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 to develop applications is not a guarantee of 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, PHP hardening is an ongoing process that must be reviewed and updated regularly. Only then can PHP applications and servers remain protected against new threats. With the right techniques and tools, together with continuous review, PHP hardening can be successfully implemented and the security of PHP applications and servers improved.

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

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