The WordPress community relies heavily on plugins to extend the functionality of the core platform. With thousands of plugins available, it's essential to ensure each plugin is secure and robust enough for use on live websites. One such plugin that helps webmasters import various content is "Import any XML or CSV File to WordPress"; however, a recent vulnerability was discovered in versions of the plugin before 3.6.9. Designated as CVE-2022-3418, this vulnerability allows administrators in multi-site WordPress installations to upload arbitrary files due to insufficient file extension filtering.

By exploiting this vulnerability, a malicious user could potentially gain unauthorized access to the underlying system and compromise the WordPress site. This long read post will discuss the vulnerability in detail, provide code snippets and solutions for mitigating the issue, as well as links to relevant references and resources.

The Vulnerability

The main issue with CVE-2022-3418 lies in the plugin's improper filtering of file extensions when uploading XML or CSV files. The source code of the affected plugin version reveals that the function responsible for handling file uploads does not adequately restrict the allowed file types, potentially enabling an attacker to upload files with malicious scripts or other harmful content.

The following code snippet demonstrates the problematic function in the plugin

function handle_import_file_upload() {
    // Check if the _wpnonce exists and if it's valid.
    if (!isset($_POST["_wpnonce"]) || !wp_verify_nonce($_POST["_wpnonce"], "handle_import_file_upload")) {
        return;
    }

    // Get the submitted file.
    $uploaded_file = $_FILES["import"];
    
    // Check for valid file extension (missing proper validation).
    // Function should only allow .xml and .csv files.
    if (preg_match("/\.(xml|csv)$/i", $uploaded_file["name"]) === false) {
        return;
    }
    
    // Check for any errors.
    // Continue with the file upload process.
}

The code does not perform a strict check on the allowed file extensions, opening the door for malicious files to be uploaded. Furthermore, it's crucial to highlight that this vulnerability primarily affects multi-site WordPress installations where multiple users with administrative privileges are present, providing a broader attack surface for potential exploitation.

Mitigation

To mitigate this vulnerability, it's strongly advised to update the "Import any XML or CSV File to WordPress" plugin to version 3.6.9 or later. The plugin developers have implemented proper file extension filtering to prevent unauthorized file uploads effectively.

Additionally, consider adding the following code to the aforementioned handle_import_file_upload() function to include a stronger validation check:

// Replace the following line:
if (preg_match("/\.(xml|csv)$/i", $uploaded_file["name"]) === false) {
    return;
}

// With:
$allowed_extensions = array('xml', 'csv');
$file_extension = pathinfo($uploaded_file["name"], PATHINFO_EXTENSION);
if (!in_array($file_extension, $allowed_extensions)) {
    return;
}

For more information on the CVE-2022-3418 vulnerability, consult the following resources

1. National Vulnerability Database (NVD) Entry: https://nvd.nist.gov/vuln/detail/CVE-2022-3418
2. Import any XML or CSV File to WordPress Plugin: https://wordpress.org/plugins/wp-all-import/
3. WordPress Plugin Security Best Practices: https://developer.wordpress.org/plugins/security/

Conclusion

As with any software, WordPress plugins can contain vulnerabilities that put websites and user data at risk. It's vital to employ best practices when developing plugins and regularly update them to minimize the potential impact of security issues. The CVE-2022-3418 vulnerability in the "Import any XML or CSV File to WordPress" plugin is a prime example of why proper file validation and security measures should always be implemented within WordPress plugins.

Timeline

Published on: 11/07/2022 10:15:00 UTC
Last modified on: 11/09/2022 20:06:00 UTC