What you should know about PHP code security

When it comes to web development, PHP is a widely used scripting language. With its popularity, it is crucial to understand the potential security risks associated with PHP and the measures to mitigate them. Whether you deploy CMS applications using WordPress or build enterprise applications with the Laravel PHP framework, the importance of PHP security and the business impact of some notable PHP interpreter vulnerabilities are crucial for developers to get right.

Why is it important to protect against PHP security vulnerabilities? Due to its popularity and wide usage, PHP is often a target for hackers and malicious entities. Security vulnerabilities can creep in due to various reasons, such as poor coding practices, lack of sanitization of user inputs, and outdated versions.

For instance, let's consider a scenario where unsanitized user input is used in a SQL query. This can lead to SQL Injection, a common vulnerability.

$id = $_GET['id'];
$sql = "SELECT * FROM users WHERE id = $id";

In the given code, a malicious user can manipulate the id parameter in the URL to perform SQL Injection. To prevent this, it is crucial to sanitize user inputs, for example, using mysqli_real_escape_string or prepared statements:

$id = mysqli_real_escape_string($conn, $_GET['id']);
$sql = "SELECT * FROM users WHERE id = $id";

Security vulnerabilities in your PHP applications can have a profound impact on your business. They can lead to data breaches, which could result in hefty fines due to non-compliance with data protection regulations, such as GDPR and CCPA. A breach can also erode customer trust, leading to a loss of business. Moreover, remediation costs to fix vulnerabilities can be high, particularly if they are identified late in the development lifecycle — which is why it’s crucial to make security a priority from the start of the project.

Related FAQs

How can I protect my PHP application from vulnerabilities?

Always validate and sanitize user input. Use prepared statements with parameterized queries to prevent SQL injection. Use the latest versions of PHP and its frameworks, as they come with security patches for known vulnerabilities. Regularly use tools like Snyk to scan your code and application dependencies and cloud infrastructure configuration for vulnerabilities. Follow secure coding practices.

Why is PHP security important?

PHP security is crucial because a vulnerable PHP application can lead to data breaches, loss of customer trust, and regulatory fines. As PHP is often used for developing web applications, it's frequently targeted by attackers. Ensuring your PHP code is secure helps protect your users' data and your business.

What is a PHP vulnerability scanner?

A PHP vulnerability scanner is a tool that automatically scans your PHP code for known security vulnerabilities. Examples include Snyk and Composer's built-in security checker. These tools can help you identify and fix security issues in your PHP applications.

What is a PHP security advisory?

A PHP security advisory is a public announcement about a security vulnerability in a PHP component. It provides details about the vulnerability, its potential impact, and how to fix it. PHP.net and other PHP-related websites often publish these advisories. Snyk also maintains a database of PHP security advisories based on the Composer package manager.

Common PHP security vulnerabilities

Let’s explore some common PHP security vulnerabilities and learn about helpful developer security resources to mitigate them.

Cookies and session management

Cookies and sessions are fundamental aspects of web development that allow us to maintain state between requests. However, if not managed correctly, they can introduce serious security flaws.

In PHP, especially when using a web framework like Laravel, it's important to secure your cookies and session data when you manage authentication. Here are some tips:

• Always use secure, HTTP-only cookies.
• Prefer setting the SameSite attribute to Lax or Strict to prevent cross-site request forgery (CSRF) attacks.
• Regenerate session ID after login or password change to avoid session fixation attack.

In Laravel, you can set these configurations in your config/session.php file:

'cookie' => env(
    'SESSION_COOKIE',
    Str::slug(env('APP_NAME', 'laravel'), '_').'_session'
),
'cookie_secure' => env('SESSION_SECURE_COOKIE', null),
'cookie_same_site' => 'lax',

Refer to more web security guidelines about securing Laravel applications to help protect against PHP security vulnerabilities.

SQL injection

SQL injection is a code injection technique that attackers use to exploit vulnerabilities in a web application's database query. It can lead to unauthorized access to sensitive data and potential manipulation or deletion of data.

Consider the following vulnerable PHP code:

$id = $_GET['id'];
$result = mysqli_query($con, "SELECT * FROM users WHERE id = $id");

An attacker can manipulate the id parameter in the URL to alter the SQL query. To prevent this, use prepared statements:

$stmt = $conn->prepare("SELECT * FROM users WHERE id = ?");
$stmt->bind_param("s", $_GET['id']);
$stmt->execute();

For more on SQL injection and PHP security, check out this free PHP security education.

Code injection

Code injection is another common vulnerability where an attacker can inject and execute arbitrary code within your application. In PHP, this often occurs when user input is passed into the eval() function or system calls without proper validation or sanitization.

Let's consider the following use case in the context of a PHP Laravel project, where a developer faced a challenge while attempting to dynamically generate an image URL within a Blade template. The goal was to display an image whose path was constructed using variable content and Laravel's URL helper function. To achieve this, the developer used PHP's eval() function as follows:

php
  eval("\$image_url = \"{{ url('public/uploads/trust/".$value.".jpg') }}\";");
?

![]({{ $image_url }})

The developer's intention was to create a flexible way to generate image URLs based on the $value variable. However, the use of eval() raises significant security concerns, such as:

• Code injection: If an attacker can influence the content of the string passed to eval(), they may execute arbitrary PHP code on the server. This could lead to unauthorized access, data breaches, and a range of other security issues.
• Complex debugging and maintenance: Code executed via eval() is often harder to debug and maintain, as it can obscure the logic and flow of the application. This complexity can inadvertently introduce additional security flaws or bugs.

The developer could have used a more secure and maintainable approach by using Laravel's Blade templating engine to generate the image URL:

![]({{ url('public/uploads/trust/'.$value.'.jpg') }})

This method avoids the use of eval() altogether, leveraging Laravel's built-in functionalities to securely generate dynamic content. Make sure you read about more ways to prevent PHP code injection.

Testing PHP Composer dependencies for security vulnerabilities

One often overlooked area of application security is third-party dependencies. In PHP, we use Composer to manage these dependencies. It's crucial to regularly check your dependencies for known security vulnerabilities.

You can use tools like Snyk to automatically scan your Composer dependencies for known vulnerabilities. Here's how you can install and use Snyk:

npm install -g snyk
snyk test

When running the snyk test command in the root directory to test your Composer dependencies for security vulnerabilities, you might see output like this:

Testing /path/to/your/laravel-project/composer.lock...

✗ High severity vulnerability found in symfony/http-foundation
  Description: Arbitrary Code Execution
  Info: https://snyk.io/vuln/SNYK-PHP-SYMFONY-174006
  Introduced through: symfony/http-foundation@5.4.0
  From: symfony/http-foundation@5.4.0
  From: symfony/http-foundation@5.4.0 > symfony/http-foundation@5.4.0
  From: symfony/http-foundation@5.4.0 > symfony/http-foundation@5.4.0 > symfony/http-foundation@5.4.0
  From: symfony/http-foundation@5.4.0 > symfony/http-foundation@5.4.0 > symfony/http-foundation@5.4.0 > symfony/http-foundation@5.4.0
  Fix: Upgrade to symfony/http-foundation@5.4.1

Tested 123 dependencies for known vulnerabilities, found 1 vulnerabilities, 122 vulnerable paths.

I highly recommend reading more on testing your PHP Composer dependencies for security vulnerabilities with Snyk.

Security vulnerabilities in the PHP interpreter

Even if you follow secure coding practices, vulnerabilities in the PHP interpreter itself can expose your applications to risks. For instance, multiple vulnerabilities were reported in the Debian PHP8.2 package, which you can view in the Snyk database.

Some of the notable PHP interpreter vulnerabilities include:

• CVE-2023-0568: Allocation of Resources Without Limits or Throttling.
• CVE-2023-3823: XML External Entity (XXE) Injection.
• CVE-2023-0662: Resource Exhaustion.

These vulnerabilities could allow an attacker to execute arbitrary code or cause a DoS (Denial of Service). So, it is essential to keep your PHP version updated and frequently check for any reported vulnerabilities in the PHP interpreter you are using.

How does Snyk help in PHP security?

Snyk is a powerful developer-first security platform that helps developers identify and fix security vulnerabilities in their PHP applications. It provides an extensive database of known vulnerabilities and can automatically scan your project for these issues. Snyk also offers automated fix PRs, which can save developers significant time in fixing identified vulnerabilities.

What are the most common PHP vulnerabilities?

There are several common PHP vulnerabilities that developers should be aware of. These include:

What’s next for PHP security?

One way to stay updated on PHP interpreter vulnerabilities is to connect your Git repositories to Snyk, which will automatically monitor your dependencies for vulnerabilities and notify you of any new vulnerabilities that are reported. Specifically, you might be deploying your PHP applications using Docker and other containerization technology, and it's crucial to monitor your container images for vulnerabilities because these Docker container images bundle the PHP interpreter and other dependencies that could be vulnerable.

If you're using Docker, you can use Snyk to scan your Docker container images for known vulnerabilities by running the following:

snyk container test your-docker-image

Make sure to follow James Walker's best practices for building a production-ready Dockerfile for PHP applications and Neema Muganga's Securing PHP Containers guide to secure your PHP container images.

Protecting against PHP security vulnerabilities should not be an afterthought but an integral part of your development process. It involves secure coding practices, regular updates, and vigilance for any reported vulnerabilities in the PHP ecosystem.

How can I learn more about PHP security?

To learn more about PHP security, you can follow online tutorials on the Snyk blog and take free online byte-sized lessons on Snyk Learn. Websites like OWASP also provide extensive resources on web application security, including PHP.