If you’ve worked with PHP for a while, you’re probably familiar with the serialize() and unserialize() functions. These are used to convert complex data structures into a string, making it easier to store or pass around. Laravel itself uses these functions in several areas. However, these functions can be quite risky if misused.

The Risks of serialize() and unserialize()

While serialize() and unserialize() can be useful, they present significant security risks. These functions can transform any data into a string and back into its original value, including classes and objects. This means that, under the right conditions, malicious users could manipulate serialized data passed through the browser.

When the unserialize() function decodes data, it reconstructs any objects embedded within the string and triggers any __unserialize() or __wakeup() methods. These methods can potentially execute malicious code (such as remote code execution or RCE) in the app, leading to serious security vulnerabilities.

How to Protect Your Code

To mitigate these risks, it’s best to avoid using serialize() and unserialize() with user-controlled data. Instead, for passing complex data structures, use safer alternatives like json_encode() and json_decode(). These functions are safer when data needs to be transmitted through the browser and cannot be tampered with.

It’s important to note that serialize() and unserialize() still have their uses in certain situations. However, when it comes to user-provided data, avoid them at all costs.

Example Scenario: Using serialize() and unserialize()

Imagine an app that uses serialize() to store user settings. The data might look like this:

Serialize example:

This turns the array into a serialized string, like:

To restore the original array, unserialize() is used:

Unserialize example:

This returns the original array:

While this works in an isolated environment, if the data is passed through the browser, an attacker could modify the serialized payload. They could use tools like PHPGGC (PHP Generic Gadget Chains) to inject malicious PHP code, causing the application to execute harmful commands.

For example, this malicious payload could expose sensitive configuration data:

This would reveal all application configuration data, including sensitive API keys and database credentials.

A Safer Approach

To prevent such risks, Laravel’s secure methods (like cookie encryption) ensure that values are protected. You should also use encryption for user data instead of relying on insecure serialization.

For added protection, always prefer json_encode() and json_decode() when transferring data through the browser. These functions are safe for handling user data, as they don't allow the same kind of manipulation that serialize() and unserialize() enable.

Want to Improve Your Laravel Security?

To take your Laravel security knowledge to the next level, check out the Practical Laravel Security Course. It covers common vulnerabilities and teaches you how to protect your applications using real-world examples and interactive challenges.

Also, if you want a professional security audit for your Laravel app, I offer Laravel Security Audits and Penetration Testing to help you secure your applications before attackers find vulnerabilities.