In this long read post, we will explore CVE-2023-0662, a newly discovered vulnerability in PHP 8..X before 8..28, 8.1.X before 8.1.16, and 8.2.X before 8.2.3. This vulnerability revolves around an excessive number of parts in HTTP form uploads, leading to high resource consumption, an overwhelming number of log entries, and ultimately causing denial of service (DoS) on the affected server. We will examine the details of the exploit, provide code snippets showcasing the issue, and link to original references and resources.

Exploit Details

The vulnerability originates from the fact that attackers can abuse the HTTP form upload system to send an unusually large number of parts or fields in a single HTTP request. This causes the server to consume excessive amounts of CPU resources and generates numerous log entries, potentially overwhelming the server's resources, and leading to a denial of service.

To put it simply, an attacker might send an HTTP form upload containing thousands or even millions of individual parts in a single request to a server running a vulnerable version of PHP. The server would then struggle to process this massive amount of data, resulting in a potential DoS.

The following code snippet demonstrates a vulnerable HTTP form upload in PHP

<?php
if ($_SERVER['REQUEST_METHOD'] == 'POST') {
    $uploaded_files = ;
    
    foreach ($_FILES as $file) {
        if (move_uploaded_file($file['tmp_name'], 'uploads/' . $file['name'])) {
            $uploaded_files++;
        }
    }
    
    echo "Successfully uploaded " . $uploaded_files . " files.";
}
?>

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>File Upload Form</title>
</head>
<body>
    <form action="upload.php" method="POST" enctype="multipart/form-data">
        <input type="file" name="files[]" multiple>
        <button type="submit">Upload files</button>
    </form>
</body>
</html>

This example PHP code demonstrates a simple form that allows the user to upload multiple files simultaneously. An attacker could potentially exploit this code by uploading a form with an excessive number of file parts.

Original References and Resources

- Official PHP 8..28 Release Notes
- Official PHP 8.1.16 Release Notes
- Official PHP 8.2.3 Release Notes
- CVE-2023-0662 Details on NIST NVD

Mitigation and Recommendations

To address this vulnerability, it is highly recommended that you update your PHP installation to one of the following patched versions:

PHP 8.2.3

In addition to updating PHP to a secure version, you should also consider implementing the following security measures:

1. Set a limit for the number of uploaded parts or fields in a single HTTP request to a reasonable number that meets your application's requirements.

Conclusion

CVE-2023-0662 is a significant vulnerability that could potentially expose PHP servers to denial of service attacks. It is crucial to keep your PHP installation up-to-date and follow best practices for securing your web applications. By staying informed and proactive in addressing security issues like this, you can help protect your server and site visitors from potential harm.

Timeline

Published on: 02/16/2023 07:15:00 UTC
Last modified on: 02/24/2023 18:09:00 UTC