What is PHAR Deserialization? The Exploit Every PHP Developer Should Know

One of the core competencies required of top PHP developers is the ability to keep up with new vulnerabilities, recognize them, and avoid coding practices that make it easier for hackers to get in. 

PHAR files, often used in PHP, can become the subject of PHAR deserialization — an exploit that can significantly harm applications and data. PHP developers need to take the time to understand this potential issue so they can guard against it. This post will explain PHAR Files and the threat PHAR deserialization presents. Let’s go. 

PHAR Files

What is a PHAR file?

A PHAR file, short for PHP Archive, is a way to bundle PHP scripts and resources into a single file. It helps developers package and distribute their applications more easily. Instead of handling many files, you only need to work with one. This can make deployment and updates simpler.

Structure and components of PHAR files

PHAR files are made up of three main parts: the stub, the manifest, and the contents. The stub is the code that runs when you execute the PHAR file. It acts like an entry point. The manifest holds metadata about the archive, such as its version and any required extensions. The contents are the actual files and directories included in the archive. This structure helps keep everything organized and easy to manage.

Advantages of using PHAR files in PHP applications

PHAR files simplify the distribution and deployment of PHP applications. By bundling all necessary files into one archive, they reduce the complexity of managing multiple files. This makes it easier to share and install applications. PHAR files also support compression, which can save space and speed up loading times. Additionally, they allow for digital signatures, adding a layer of security by ensuring the integrity and authenticity of the code.

Common uses of PHAR files in real-world applications

PHAR files are used in many real-world applications. Developers use them to package tools, libraries, and frameworks for easier distribution. For example, Composer, a popular dependency manager for PHP, uses PHAR to distribute its executables. 

This approach simplifies installation and updates. Similarly, developers might bundle custom scripts and resources in a PHAR file to create a single, executable package for their applications, streamlining deployment and reducing the risk of missing files.

Serialization and deserialization in PHP

What is serialization in PHP?

Serialization in PHP is the process of converting a data structure or object into a format that can be easily stored or transmitted. The serialized data can be saved in a file, sent over a network, or stored in a database. 

Common use cases include saving user sessions, caching data, and preparing objects for transfer between different parts of an application. Serialization makes it possible to store complex data structures in a simple, linear form.

What is deserialization in PHP?

Deserialization in PHP is the process of converting serialized data back into its original data structure or object. This is essential for retrieving and using data that was previously serialized and stored or transmitted. 

Common use cases include reading session data, loading cached data, and receiving complex data structures from APIs or other sources. Deserialization allows applications to reconstruct data as it was before serialization, making it usable again.

Why deserialization can be dangerous

Deserialization can be dangerous because it allows data to be turned back into executable code. If an attacker can manipulate the serialized data, they can inject malicious code. This can lead to various security issues like remote code execution, data tampering, and unauthorized access. 

Deserialization vulnerabilities are especially concerning because they can be exploited even if the attacker doesn’t have direct access to the server. Ensuring proper validation and handling of serialized data is crucial to prevent these risks.

PHAR deserialization

What is PHAR deserialization?

PHAR deserialization is the process where serialized data inside a PHAR file is converted back into PHP objects. This can be useful for extracting data and executing code stored in the archive. However, it also introduces risks. If an attacker can modify the PHAR file, they can inject malicious code that gets executed during the deserialization process. This makes PHAR deserialization a potential security threat if not handled properly.

How PHAR deserialization works

PHAR deserialization involves several steps. First, the PHAR file is accessed, and its contents are read. The PHP code inside the PHAR file is then extracted. During this process, any serialized data within the PHAR file is identified. 

This data is then converted back into PHP objects through deserialization. If the serialized data has been tampered with, it can include malicious code that gets executed when deserialized. This is why it is crucial to ensure that PHAR files are not altered by unauthorized users.

PHAR deserialization and WordPress

The role of PHP in WordPress

PHP is the core programming language used by WordPress. It powers all the backend functionality, from processing form submissions to connecting with the database. WordPress themes and plugins are also written in PHP. This makes it a critical part of the WordPress ecosystem. 

PHP handles everything from generating page content to managing user sessions. Its flexibility and wide usage make it a key component in WordPress development and maintenance.

How WordPress uses PHAR files

WordPress itself does not commonly use PHAR files directly. However, some plugins and themes might use them to bundle code and resources. This can simplify the distribution and installation process for these plugins and themes. 

Developers might opt for PHAR files to incorporate multiple files in a single package, ensuring all necessary components are included. While not a standard practice in core WordPress development, the use of PHAR files in plugins and themes can still expose sites to potential security risks if not handled properly.

Potential risks of PHAR deserialization for WordPress sites

PHAR deserialization poses several risks for WordPress sites. If an attacker can upload or modify a PHAR file, they can inject harmful code into the site. This can lead to remote code execution, where the attacker gains control over the server. 

Other risks include data breaches, unauthorized access, and site defacement. Because WordPress relies heavily on PHP, any vulnerability in how it handles PHAR files can be a serious security threat. Ensuring proper security measures can help mitigate these risks.

How to prevent PHAR deserialization exploits

Vulnerability scanning

Regularly scanning your website for vulnerabilities is crucial. Tools like vulnerability scanners can identify weaknesses in your code, including those related to PHAR deserialization. These scanners check for outdated software, insecure configurations, and known security flaws. 

By identifying issues early, you can take steps to fix them before they are exploited. Using a reliable, automated scanner can help maintain the security of your WordPress site.

Input validation

One of the best ways to prevent PHAR deserialization exploits is through rigorous input validation. Ensure that any data entering your system is properly sanitized and validated. This includes user inputs, file uploads, and data from external sources. By checking and cleaning this data, you reduce the risk of malicious code being introduced into your application. Input validation helps prevent attackers from injecting harmful data, making your site more secure.

Use of safe libraries and functions

Using safe libraries (groups of pre-written code templates that provide specific functionality) and functions is another important step in preventing PHAR deserialization exploits. Many libraries have built-in security features that can protect against common vulnerabilities. By relying on well-maintained libraries, you can benefit from their security updates and community support. 

Additionally, avoid using functions that are known to be unsafe or deprecated. Stick to functions that are recommended by the PHP community for handling deserialization securely.

PHP configuration settings that can mitigate risk

Adjusting PHP configuration settings is a key step in reducing the risk of PHAR deserialization exploits. One important setting is `phar.readonly`, which should be enabled to prevent modification of PHAR files. 

Another useful setting is `disable_functions`, where you can list functions that could be exploited during deserialization. Limiting file operations by adjusting the `open_basedir` setting can also help. Regularly review and update these settings to ensure they align with best security practices.

How to secure WordPress against PHAR deserialization

1. Install a reputable security plugin like Jetpack Security

One of the best ways to protect your WordPress site from PHAR deserialization exploits is by installing a reputable security plugin. Jetpack Security is a solid choice. It provides comprehensive protection against various threats, including those involving PHAR files. 

Jetpack Security offers real-time monitoring and alerts, helping you stay ahead of potential vulnerabilities. By using a trusted plugin like Jetpack Security, you can enhance your site’s security and reduce the risk of attacks.

Learn more about Jetpack Security here.

2. Make sure the plugin you choose has a vulnerability scanner

When choosing a security plugin, ensure it includes a vulnerability scanner. Jetpack Security has this feature, leveraging the WPScan database, which tracks over 50,000 known vulnerabilities.

A vulnerability scanner can identify weak spots in your WordPress site, including issues related to PHAR deserialization. By regularly scanning your site, you can detect and fix vulnerabilities before they are exploited. This proactive approach helps maintain the security and integrity of your website.

3. Keep WordPress, themes, and plugins up-to-date

Keeping your WordPress installation, themes, and plugins up-to-date is crucial for security. Updates often include patches for known vulnerabilities, including those related to PHAR deserialization. Regularly check for updates and apply them as soon as they are available. Many security issues arise from outdated software, so staying current can prevent many potential exploits. Enable automatic updates, if possible, to ensure you don’t miss critical patches.

4 Keep your PHP version up to date

Ensuring that your server runs the latest PHP version is vital for security. Each PHP update includes fixes for known vulnerabilities and performance improvements. Running an outdated version of PHP can expose your WordPress site to various risks, including PHAR deserialization exploits. Regularly check your hosting environment and apply available PHP updates promptly. This simple step helps keep your site secure and efficient.

5. Adopt a security-first mindset when developing

Developers should adopt a security-first mindset when creating WordPress sites and plugins. This means considering security at every stage of development. Validate inputs, use secure coding practices, and regularly review code for vulnerabilities. 

Being proactive about security helps prevent issues like PHAR deserialization exploits. Regular training and staying updated on the latest security practices can also make a significant difference. By making security a priority, you protect your site and its users.

6. Ensure you have reliable website backups

Reliable backups are crucial for recovering from any security incident, including PHAR deserialization exploits. Regular backups ensure you can restore your site to a previous state if it gets compromised. 

Jetpack Security offers a real-time backup solution as part of its plugin. This feature continuously backs up your site, so you always have the latest version available for restoration. By using Jetpack Security’s backup solution, you can quickly recover from attacks and minimize downtime.

Frequently asked questions

What is a PHAR file, and why is it used?

A PHAR file is a PHP Archive file that bundles multiple PHP files and resources into a single package. It simplifies the distribution and deployment of PHP applications by consolidating all necessary components into one file. PHAR files are used to ensure that all dependencies and resources are included, making it easier to share and install PHP applications.

How can PHAR files become a security risk?

PHAR files can become a security risk if they are not properly managed or validated. If an attacker can upload or modify a PHAR file, they can include malicious code that gets executed when the file is processed. This can lead to remote code execution, data breaches, and unauthorized access. PHAR deserialization exploits can occur when serialized data within the PHAR file is tampered with, allowing harmful code to run during deserialization. Ensuring that PHAR files are securely handled and validated is crucial to mitigating these risks.

What is PHAR deserialization?

PHAR deserialization is the process of converting serialized data within a PHAR file back into PHP objects. This process can be risky because if an attacker can manipulate the serialized data, they can inject malicious code. When the deserialized data is processed, the malicious code can be executed, leading to security vulnerabilities such as remote code execution or data breaches. Proper validation and handling of serialized data are essential to prevent these risks.

Why should PHP developers be concerned about PHAR deserialization vulnerabilities?

PHP developers should be concerned about PHAR deserialization vulnerabilities because they pose a significant security risk. If an attacker can exploit this vulnerability, they can inject malicious code into the application. This can lead to severe consequences like remote code execution, data theft, and unauthorized access. 

Developers need to ensure that their code properly validates and handles PHAR files to prevent these exploits. Understanding and mitigating these risks is crucial for maintaining the security of PHP applications.

How is a PHAR deserialization attack executed?

A PHAR deserialization attack is executed by manipulating serialized data within a PHAR file. An attacker first uploads a malicious PHAR file or modifies an existing one. This file contains harmful code within its serialized data. When the application deserializes this data, the code gets executed. 

This can cause security problems, like remote code execution, theft of sensitive information, and unauthorized access. Proper validation and secure handling of PHAR files are essential to prevent these attacks.

What types of applications are most at risk from PHAR deserialization?

Applications that allow users to upload files or handle serialized data are most at risk from PHAR deserialization. This includes content management systems like WordPress, forums, file-sharing platforms, and any custom PHP application that processes user-uploaded files. These applications are vulnerable if they do not properly validate and sanitize the uploaded PHAR files. Ensuring robust security practices can help mitigate these risks.

How does PHAR deserialization affect WordPress sites specifically?

PHAR deserialization affects WordPress sites by exposing them to security vulnerabilities. If an attacker can upload a malicious PHAR file to a WordPress site, they can execute harmful code when the file is deserialized. 

This can lead to unauthorized access, data theft, or even a complete site takeover. WordPress plugins and themes that handle file uploads are particularly vulnerable if they do not properly validate and sanitize PHAR files. Ensuring these components are secure is essential to protect the site.

Can plugins or themes affect the security of WordPress concerning PHAR files?

Yes, plugins and themes can affect the security of WordPress concerning PHAR files. If a plugin or theme allows users to upload files without proper validation and sanitation, it can introduce vulnerabilities. Malicious PHAR files can be uploaded and deserialized, leading to security issues like remote code execution or unauthorized access. 

Developers should ensure their plugins and themes are secure by validating and sanitizing all inputs and uploads. Regular updates and security audits can also help maintain a secure WordPress environment.

Why is a vulnerability scanner crucial in detecting PHAR deserialization vulnerabilities?

A vulnerability scanner is crucial in detecting PHAR deserialization vulnerabilities because it helps identify weak points in your site before attackers can exploit them. These scanners can detect outdated software, insecure configurations, and known vulnerabilities, including those related to PHAR deserialization. 

By regularly scanning your site, you can find and fix issues early, reducing the risk of a successful attack. Using a reliable vulnerability scanner is an essential part of maintaining a secure WordPress site.

How can Jetpack Security help prevent PHAR deserialization attacks on WordPress?

Jetpack Security helps prevent PHAR deserialization attacks on WordPress by providing a comprehensive security solution. It includes a powerful vulnerability scanner that identifies potential risks, including those related to PHAR deserialization. 

Jetpack Security also offers real-time monitoring and automatic threat resolution, ensuring that any detected vulnerabilities are addressed quickly. By using Jetpack Security, you can safeguard your WordPress site against various threats and maintain a secure environment.

Where can I learn more about Jetpack Security?

You can learn more about Jetpack Security on its official page on the Jetpack website. The page provides detailed information about the features, benefits, and pricing of Jetpack Security. You can also find user reviews, case studies, and support resources to help you understand how Jetpack Security can protect your WordPress site.

Explore Jetpack Security here: https://jetpack.com/features/security/