How to Fix 20 Common PHP Issues With AI

PHP is still one of the most popular languages for server-side scripting because it’s simple, adaptable, and backed by an extensive library of frameworks and tools. However, its widespread adoption also comes with common coding challenges that can lead to security vulnerabilities, maintainability issues, poor performance, and inferior code quality.

As a PHP developer, team lead, or software engineer, you’ll often encounter recurring issues such as SQL injection vulnerabilities, inefficient queries, poor error handling, and code duplication that can slow down the development process, introduce bugs, and expose applications to security risks if not adequately addressed.

In recent years, AI has transformed the software development lifecycle. AI code review tools like CodeRabbit automate the identification and resolution of coding issues, making it easier for programmers to write cleaner, more efficient, and more secure PHP code. These tools help you review code quality and streamline the process of identifying errors, suggesting fixes, and maintaining high standards for your source code.

This article will guide you through the following 20 common issues in PHP code and provide practical solutions using CodeRabbit as demonstrated in these pull requests: PR 1 and PR 2. By the end, you will better understand how AI can assist in fixing certain errors while improving code quality, security, and overall development productivity.

I tried to make this list as comprehensive as possible, so feel free to skip any that you’ve already addressed.

TL;DR: List of Common PHP Issues

To give you a quick glance at the issues, here’s a breakdown of the issues, grouped by their frequency, impact, and relevance to PHP development:

Critical and Often Overlooked: the issues highlighted here are some of the most impactful yet frequently underestimated by developers. Addressing them is vital for maintaining secure and efficient applications.

Insecure deserialization
Misconfigured session management
Inefficient caching
Inefficient file handling
Improper use of arrays

Important and Relevant but Often Missed: these issues might not always be obvious but can significantly affect application performance, security, and maintainability.

Security vulnerabilities
Command injection
Insecure password handling
Improper use of static methods
Cross-Origin Resource Sharing (CORS)
Poor error handling
Deprecated functions
Hardcoding configuration data

Worth Addressing for Overall Code Quality: these issues contribute to better code quality and cleaner architecture when resolved.

Uncaught fatal errors
Inefficient queries
Lack of unit tests
Memory leaks
Code duplication
Over-complicated code
Inconsistent coding style

You can fix these manually or turn to an AI tool. To implement AI-suggested fixes, sign up to Co d eR abb it and give it access to your GitHub Repo. CodeRabbit will be ready to review every pull request in the repo automatically.

Issue #1: Insecure Deserialization

Insecure deserialization occurs when untrusted data is deserialized without proper validation, allowing attackers to inject malicious data structures or manipulate application logic. Deserialization with functions like unserialize() on user-controlled data can lead to code execution, data manipulation, or privilege escalation.

// Deserialization with unserialize function

$data = $_POST['data'];
$object = unserialize($data);

As shown in the image below, with the help of AI code review tools, you can use the JSON serialization function instead of PHP serialization to avoid deserializing untrusted input, which could lead to potential security vulnerabilities

Issue #2: Misconfigured Session Management

Session management is one of those things that you might not think about until it goes wrong. Without secure session handling, your app could be vulnerable to session hijacking or unauthorized access.

// Insecure session setup

session_start();

Experienced developers typically have templates for setting up secure sessions. Automated tools can identify weak session settings and suggest improvements, such as setting secure cookies, regenerating session IDs, and implementing session timeouts. These adjustments help ensure user sessions remain safe and secure.

Alternatively, you can also

Regenerate session IDs on login to prevent session fixation.
Use secure, HTTP-only cookies for session management.
Enforce session timeouts and other security best practices.

These improvements help secure user sessions, reducing the chances of account compromise.

Issue #3: Inefficient Caching

Without caching, your app can repeatedly make the same database calls, causing slowdowns and consuming resources, especially when handling repetitive tasks like database queries or API calls.

// No caching, querying the database on every page load

$query = "SELECT * FROM posts";
$result = mysqli_query($connection, $query);

AI code review tools can help identify areas where caching can improve performance and suggest optimal strategies, as shown in the image below. This approach boosts data retrieval speed and reduces unnecessary server load."

In this case, CodeRabbit suggestions are standard practices for caching across all programming languages:

Implementing Redis or Memcached for in-memory caching.
Leveraging object caching for database queries or external API calls.

By automating the identification of caching opportunities, AI code review tools help developers improve application performance and reduce load times.

Issue #4: Inefficient File Handling

If you read or write large files all at once, you risk performance issues or even crashes. Loading large files into memory may cause high usage or even exhaust available memory.

// loading a large file into memory

$data = file_get_contents('largefile.json');

Many inefficient file I/O operations go undetected if you check manually; AI code review tools like CodeRabbit can help you identify such situations. Here is a snapshot of issues raised by the tool regarding the inefficient file handling of a large JSON file.

The tool suggests ways to write better code and improve software quality like:

Using streaming techniques to handle large files in smaller chunks.
Implementing buffering strategies to optimize file reads and writes.

This results in faster file handling, reduced memory consumption, higher quality, and improved performance.

Issue #5: Improper Use of Arrays

PHP’s dynamic arrays are powerful but can lead to performance issues if not used efficiently, especially with large datasets.


// Iterate over users array and extract name field into another array

$names = [];

foreach ($users as $user) {
    $names[] = $user['name'];
}

With automated tools, you can identify missed caching opportunities and receive suggestions for optimal alternatives to improve performance, as you have below:

Built-in functions like array_column(), array_map(), or array_filter() could be more efficient compared to loops. Optimizing array handling can significantly boost performance in PHP applications dealing with large data volumes.

Issue #6: Security Vulnerabilities

Your PHP applications often face vulnerabilities like SQL injection, Cross-Site Scripting (XSS), and Cross-Site Request Forgery (CSRF). When you do not validate or sanitize your input properly or mishandle user data, attackers can inject malicious code, compromising the entire database. Similarly, insecure session handling or lack of password hashing can expose sensitive user information, leading to potential data breaches.

Though not very common in modern applications, SQL injections are still a significant concern in applications with direct database interactions or user-generated content. Here’s a simple example of SQL injection.

// Retrieve the 'username' parameter and use it to construct a SQL query to select all columns from users

$user_input = $_GET['username'];
$query = "SELECT * FROM users WHERE username = '$user_input'";
$result = mysqli_query($connection, $query);

Directly including user inputs in SQL queries is an unsafe method of handling user input in web pages and a potential SQL injection vulnerability in the query construction.

The details provided by an automated tool are shown in the snapshots below:

The recommended actions used in standard practice are as follows:

Using prepared statements in SQL queries to prevent SQL injection.
Applying input validation and sanitization and output escaping to prevent XSS attacks.
Use Object-Relational Mapping (ORM) libraries to handle query parameterization.

Similarly, CSRF exploits the trust that a web application has in the user’s browser. When a user is authenticated, their browser automatically includes session cookies and other credentials in requests to the web application.

An attacker crafts a malicious request and tricks the user into executing it, often through social engineering techniques like sending a link via email or embedding it in a malicious website. The web application processes the request as if it were a legitimate action from the authenticated user.

// start a session and process a post request to transfer amount to a recipient (vulnerable to CSRF
session_start();

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $amount = $_POST['amount'];
    $recipient = $_POST['recipient'];

    // Process the transfer (vulnerable to CSRF)
    echo "Transferred $amount to $recipient";
}

From the image above, an automated tool detected the following security issues and suggested code improvements:

CSRF vulnerability allows unauthorized transfers
Missing input validation and sanitization
No authentication check
Potential XSS vulnerability in the echo statement

Automating these checks can drastically reduce security risks and ensure your applications are better protected against these common attacks.

Issue #7: Command Injection

Functions like exec(), shell_exec(), system(), and passthru() execute system commands and can be exploited if they incorporate user input directly dangerous. An attacker may inject malicious system commands into input fields, which can be executed by the server if there is no input validation or sanitization of user inputs.

// Running system commands with input data

$filename = $_GET['filename'];
system("rm $filename");

AI code review tools can easily detect this risky command injection vulnerability and recommend safer alternatives, such as using the unlink() function.

Issue #8: Insecure Password Handling

Storing passwords insecurely is a major risk. If you store passwords in plain text or use weak hashing algorithms, this can lead to security vulnerabilities.

// Insecure password storage

$password = md5('password123');

AI code review tools can detect insecure password storage practices and suggest using strong hashing algorithms like bcrypt or Argon2 to protect sensitive user data.

Issue #9: Improper Use of Static Methods

Overusing static methods in PHP can make code less flexible and harder to test.

// Static method overuse

class User {
    public static function getName() {
        return "John";
    }
}

Integrating automated tool helps identify the overuse of static methods, as shown below:

Refactoring the code with the following suggestions can help improve the code quality:

Converting static methods to instance methods where appropriate.
Applying object-oriented principles like polymorphism to improve code flexibility.

Cross-Origin Resource Sharing (CORS) is a security feature implemented by web browsers to control how web pages can request different domains (origins). CORS is designed to protect users by enforcing the Same-Origin Policy (SOP), which restricts web pages from requesting a different origin than the one that served the web page.

It helps prevent malicious websites from making unauthorized requests on behalf of a user, which could lead to security issues like data theft or unauthorized actions. Misconfigurations can easily lead to errors.

// Configuration that allows Cross-Origin access

header("Access-Control-Allow-Origin: *"); // Allows any domain to access the resource
header("Access-Control-Allow-Methods: GET, POST, PUT, DELETE"); // Allows all HTTP methods
header("Access-Control-Allow-Headers: *"); // Allows all headers
header("Access-Control-Allow-Credentials: true"); // Allows credentials (cookies, authorization headers, etc.)

Configuring CORS correctly can be tricky for developers. It requires configuring precise CORS settings on the server, and developers usually need to balance security with functionality. CORS issues often arise when moving from a development environment to a production environment with a different domain.

With automated tools, you can identify misconfigured CORS headers that pose security risks and receive tailored configuration suggestions, as shown in the image below:

Issue #11: Poor Error Handling

You’ve encountered code crashes, often leaving you with no valuable information to trace the problem. Inadequate error handling can make it feel like you’re chasing ghosts in your codebase as you search for the source of the issue. This often complicates debugging and negatively affects your productivity.

// File handling without any error handling

$data = file_get_contents('data.txt');

Gaps in error handling, such as missing try-catch blocks or a lack of appropriate tests for handling the situation (file handling in this case), may lead to potential errors or warnings. The file may not exist or may be inaccessible.

Other best practices can also be implemented, such as:

Wrapping potentially error-prone code (e.g., database operations, file handling) in try-catch blocks.
Logging errors and handling exceptions in a way that ensures graceful recovery.

These suggestions help improve your application's quality code and robustness, minimizing the likelihood of unhandled exceptions affecting performance or user experience.

Issue #12: Deprecated Functions

Using deprecated functions is like walking on thin ice—they might work now but can break in future PHP versions.

// Use of deprecated function split() for splitting string

$var = split(',', $string);

Automated review tools can automatically flag deprecated functions and suggest modern alternatives, ensuring your code is future-proof and less vulnerable to compatibility issues.

Issue #13: Hardcoding Configuration Data

Hardcoding sensitive data (e.g., database credentials, API keys) in your PHP files poses security risks, especially when your code is shared or deployed. Hardcoding configuration data is generally considered an anti-pattern due to known security and maintainability issues.

$API_KEY = 'ThisISsomeRandomAPIKey'

With modern secrets management tools such as AWS Secrets Manager, Azure Key Vault, or HashiCorp Vault, this is rare. However, many new developers might hardcode certain configurations directly into source code due to the perceived simplicity of hardcoding. Some of the most common hard-coded configurations are:

Database credentials such as host, database name, even username and password.
API Keys and tokens for third-party services.
File paths and URLs to important files or directories
Application settings and flags.

As shown below, automated tools can detect hardcoded values in your PHP code and recommend secure alternatives, such as using environment variables or secrets management systems.

Here are some recommended best practices and tool to handle configuration and credentials:

Storing sensitive data in environment variables or configuration files.
Using tools like dotenv to load environment variables securely.

Issue #14: Uncaught Fatal Errors

Uncaught fatal errors, such as those caused by missing functions or classes, can crash an entire PHP application. These errors make the system unavailable until the issue is resolved, leaving users with a frustrating experience.

// Fatal error due to undefined function

$result = getUserDetails;

AI tools can scan for areas where fatal errors might occur and suggest ways to handle them better, making your application run more smoothly.

In such situations, as we have in the image above, the recommendation is to:

Implementing a global error handler to catch fatal errors.
Using custom error handling functions to log issues and present user-friendly error pages rather than crashing the application.

This ensures that your application can remain operational and user-friendly even in a serious error.

Issue #15: Inefficient Database Queries

Inefficient database queries are a common bottleneck for your app’s performance. If you’re fetching too much data, running unnecessary joins, or missing crucial indexes, your app can end up painfully slow. Such unoptimized database queries can lead to performance bottlenecks and scalability issues, particularly when dealing with large datasets.

// Inefficient database query: selecting all

$query = "SELECT * FROM users";
$result = mysqli_query($connection, $query);

Identifying these inefficient queries can be challenging, but this issue can be optimized by adding indexes or fetching only the necessary columns. Through such optimization, you can keep your app running fast and smoothly, even under heavy loads.

Code review tools can help analyze your database queries for inefficiencies such as:

Unoptimized SELECT queries that fetch unnecessary data.
Missing or inappropriate use of indexes.

It suggests query optimizations, such as adding appropriate indexes, reducing the number of table joins, and selecting only the required columns.

Issue #16: Lack of Unit Tests

Testing might not be the most exciting part of coding, but it’s essential for ensuring reliability. Skipping tests often leads to bugs slipping into production, making maintaining code quality challenging.

// function to add two numbers

function add($a, $b) {
    return $a + $b;
}

Automated tools like CodeRabbit can highlight areas of your codebase that lack test coverage.

It is usually recommended to:

Write unit tests for every critical logic.
Use testing frameworks like PHPUnit to ensure the reliability of your code

By automating the process of identifying untested code, these tools make your code more reliable and easier to maintain.

Issue #17: Memory Leaks

Memory leaks can quietly consume server resources, especially if you don’t close database connections or release resources.

// Memory leak due to unclosed connection

$connection = new mysqli($host, $user, $pass, $db);

Automated review tools can detect potential memory leaks by analyzing your code for inefficient use of resources (e.g., large object allocations not being freed).

It suggests solutions like:

Properly closing database connections and file handles.
Using tools like Garbage Collection more effectively.

This helps maintain the performance and scalability of your application, especially under heavy load.

Issue #18: Code Duplication

You've likely copied and pasted codes and unintentionally created a mess of duplicated business logic throughout your project. Repeated blocks of code across a project lead to higher maintenance costs and increase the chances of bugs when changes are made.

The following code consists of code duplication logic for connecting to the database, executing a query, and processing the results, which is repeated for fetching user and product data.


// Fetch user data

$conn = connectDatabase();
$sql = "SELECT * FROM users";
$result = $conn->query($sql);
if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo "User: " . $row["username"] . "<br>";
    }
}
$conn->close();

// Fetch product data
$conn = connectDatabase();
$sql = "SELECT * FROM products";
$result = $conn->query($sql);
if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo "Product: " . $row["product_name"] . "<br>";
    }
}
$conn->close();

Duplicate code logic increases the risk of bugs and the effort required to maintain the code. Refactoring the code by eliminating redundant sections with reusable functions or classes can improve the code quality. This keeps your codebase DRY (Don’t Repeat Yourself) and less error-prone.

AI code review tools like CodeRabbit promote the (Don't Repeat Yourself) DRY principle by:

Identifying sections of duplicated logic.
Recommending ways to consolidate common functionality into reusable functions or classes.

This reduces redundancies and makes future maintenance easier and less error-prone.

Issue #19: Over-Complicated Code

Sometimes, your code becomes overly complex with deeply nested loops or conditionals, making it hard to read, debug, and maintain, leading to potential issues as your project evolves.

// Complex nested conditionals

if ($a == 1) {
    if ($b == 2) {
        if ($c == 3) {
            echo "Success";
        }
    }
}

You can manually assess the code’s complexity, but this is time-consuming. This is where an AI code review tool like CodeRabbit can be really helpful.

You could improve the code complexity by:

Breaking large functions into smaller, more manageable ones.
Reducing deeply nested loops or conditionals.

Simpler code is easier to maintain, which reduces the likelihood of future bugs and makes your application more scalable.

Issue #20: Inconsistent Coding Style

Inconsistent coding styles can make your team projects messy and make collaboration difficult. With varying indentation, naming conventions, and formatting, the codebase can quickly become disorganized.

// Non-conventional function naming style

function get_user_Data() {
    return "User data";
}

Like some popular PHP linting tools, such as PHP_CodeSniffer and PHPStan, automated tools also offer automatic formatting and style consistency checks based on popular coding standards, such as PSR-2 and PSR-12.

By enforcing consistent coding and development practices, you can:

Ensure cleaner, more readable code.
Reduce friction when collaborating with other developers.

What’s Next?

While this article has covered 20 common PHP issues and how AI tool like CodeRabbit addresses them, several additional challenges deserve your attention:

Advanced Error Reporting: As applications scale, error reporting and monitoring tools like Datadog become important. Look into integrating AI-driven monitoring solutions for a proactive approach.
Version Updates: PHP versions are released with updates that enhance security and performance. Tracking these updates by visiting the official PHP Release Page and keeping your applications current is effective for staying ahead of vulnerabilities.

Adopting these strategies can further enhance the quality of your PHP projects and prepare your applications for long-term success.

Conclusion

Developing robust PHP applications requires addressing a range of considerations, from optimizing performance to ensuring code quality and security. Addressing these problems manually can be time-consuming and error-prone, especially as applications grow in size and complexity. However, AI tools like CodeRabbit simplify this by automating the detection and resolution of common PHP issues, saving time and improving development efficiency.

From improving security by eliminating vulnerabilities like SQL injection to enhancing code quality, this article explored 20 scenarios where CodeRabbit can significantly simplify the development process. Integrated with your repository, it automates code reviews in pull requests, identifies potential issues, and supports thorough testing and debugging.

Sign up to CodeRabbit for a free trial and experience automatic reviews that enhance your application's quality while helping your team work faster and better. You can also join the Discord channel to connect with a community of developers, share insights, and discuss the projects you're working on.