What are potential security risks associated with allowing users to upload images in PHP applications?

Allowing users to upload images in PHP applications can pose security risks such as file upload vulnerabilities, potential execution of malicious code, and server overload with large files. To mitigate these risks, it is important to validate and sanitize user input, restrict file types and sizes, and store uploaded files outside of the web root directory. 

// Example code snippet to validate and sanitize uploaded image file
$target_dir = "uploads/";
$target_file = $target_dir . basename($_FILES["file"]["name"]);
$imageFileType = strtolower(pathinfo($target_file,PATHINFO_EXTENSION));

// Check if file is an actual image
if(isset($_POST["submit"])) {
    $check = getimagesize($_FILES["file"]["tmp_name"]);
    if($check !== false) {
        move_uploaded_file($_FILES["file"]["tmp_name"], $target_file);
        echo "File is a valid image.";
    } else {
        echo "File is not an image.";
    }
}

Keywords

file upload vulnerability image validation file extension checking image manipulation functions cross-site scripting

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