Is Your Laravel Application at Risk? The register_argc_argv Vulnerability Explained

After receiving a GitHub notification about a security advisory affecting my public repositories, I found myself asking, “What the hell is that? and How a Simple PHP Setting Can Lead to Major Security Risks in Laravel”

In this post, I won’t focus on how to exploit this issue; instead, I want to discuss just how dangerous it can be.

Disclaimer: I’m not sure how anyone might exploit this in a real-world scenario, but I’ll provide a theoretical example to illustrate the potential risks.

Who Is Affected?

If you’re using a PHP-FPM Docker image and haven’t set an implicit php.ini file, you might be affected.

How to Check

The simplest way to check if you’re affected is to create a file named phpinfo.php with the following content:

<?php
   phpinfo();
?>

Open this file in your browser and look for the register_argc_argv setting. If it’s set to "On," you could be at risk.

What Is register_argc_argv?

According to the official PHP documentation, register_argc_argv tells:

PHP whether to declare the argv and argc variables (which would contain the GET information). See also command line.

In simpler terms, this means you can manipulate environment variables through normal GET requests!

Affected Versions

The vulnerability affects the following Laravel versions:

< 6.20.45
= 7.0.0, < 7.30.7
= 8.0.0, < 8.83.28
= 9.0.0, < 9.52.17
= 10.0.0, < 10.48.23
= 11.0.0, < 11.31.0

If you are using any of these versions, it is crucial to take action.

The Fix “Environment Manipulation via Query String” issue with updating your laravel version:

The Laravel team has addressed this vulnerability in the following patched versions:

• 6.20.45
• 7.30.7
• 8.83.28
• 9.52.17
• 10.48.23
• 11.31.0

The fix involves modifying how the framework handles environment detection. In the patched versions, Laravel now ignores argv values for environment detection on non-CLI Server Application Programming Interfaces (SAPIs), effectively mitigating the risk.

A Practical Example

Let’s say you have a Laravel application running at app.domain.com. An attacker could potentially change your environment variables, such as APP_ENV, by crafting URLs like:

app.domain.com/home?--env=local
app.domain.com/home?APP_NAME=local
app.domain.com/home?--env="APP_NAME=local"

The Risks with Laravel Horizon

Now, consider that you have multiple background jobs and are using Horizon for load balancing. This is a common setup, but it can introduce vulnerabilities.

Let’s explore how this vulnerability could be exploited to access sensitive information within your application.

When your application is running in a local environment, Horizon typically bypasses authentication (e.g., when using php artisan serve or composer dev).

Imagine a scenario where a user discovers that your Horizon dashboard is accessible at app.domain.com/horizon/dashboard and opens it.

Wait, What!?

Yes, in theory, it’s possible to change the environment to local and bypass authentication for the dashboard.

The Consequences

Let’s look at a job I created that sends an email to a user:

public function handle()
{
    Mail::to($this->user->email)->send(new UserEmail($this->user));
}

The constructor of this job looks like this:

public function __construct(protected User $user){}

At first glance, this seems secure, but consider what happens when you pass implicit variables (like integers, strings, booleans, floats, or arrays).

In the logs, you might see:

This shows all the information that you would normally want to keep secure, now exposed!

Conclusion

The register_argc_argv vulnerability is a stark reminder of the importance of securing your applications and understanding the implications of PHP configurations. Always ensure your environment is properly configured and stay informed about potential vulnerabilities in the frameworks you use.

By being proactive, you can help protect your applications from exploitation.