CVE-2015-9521 in Pushover Notifications Extension
Summary
by MITRE
The Easy Digital Downloads (EDD) Pushover Notifications extension for WordPress, as used with EDD 1.8.x before 1.8.7, 1.9.x before 1.9.10, 2.0.x before 2.0.5, 2.1.x before 2.1.11, 2.2.x before 2.2.9, and 2.3.x before 2.3.7, has XSS because add_query_arg is misused.
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Analysis
by VulDB Data Team • 02/08/2025
The CVE-2015-9521 vulnerability affects the Easy Digital Downloads Pushover Notifications extension for WordPress, representing a cross-site scripting flaw that emerged due to improper handling of URL parameters within the extension's codebase. This vulnerability specifically impacts versions of Easy Digital Downloads ranging from 1.8.x through 2.3.x, before their respective security patches were released, making it a widespread issue across multiple version lines of the popular WordPress e-commerce plugin. The flaw stems from the misuse of the add_query_arg WordPress function, which is designed to safely manipulate URL query parameters but was incorrectly implemented in this extension, creating opportunities for malicious actors to inject harmful scripts into the application's response.
The technical implementation of this vulnerability occurs when the extension processes user-supplied input through URL parameters that are then passed to add_query_arg without proper sanitization or validation. When a malicious user crafts a specially crafted URL with XSS payload in the query string, the extension fails to properly escape or validate this input before rendering it in the browser context. This misconfiguration allows attackers to inject malicious JavaScript code that executes in the context of other users' browsers who visit the affected pages. The vulnerability is classified as CWE-79, which represents Cross-Site Scripting, and specifically aligns with the attack pattern where untrusted data flows into web output without proper sanitization. The flaw operates at the application layer, specifically affecting the user interface rendering process where URL parameters are consumed and displayed without adequate security controls.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable attackers to perform various malicious activities including session hijacking, credential theft, and data exfiltration. An attacker could craft malicious URLs that, when clicked by an administrator or other privileged user, would execute scripts that steal cookies, modify site content, or redirect users to phishing sites. This vulnerability particularly threatens WordPress sites using Easy Digital Downloads because it allows attackers to exploit the extension's functionality without requiring authentication, making it a server-side vulnerability that can be exploited from outside the network. The attack surface is broad since the extension is commonly used across numerous WordPress installations, and the XSS payload could be designed to target various user roles, from regular customers to site administrators. The vulnerability's persistence is enhanced by the fact that it operates through legitimate URL parameter processing, making it difficult to distinguish from normal application behavior and harder to detect through standard security monitoring.
Mitigation strategies for CVE-2015-9521 focus on both immediate remediation and long-term security hardening measures. The primary solution involves updating the affected Easy Digital Downloads Pushover Notifications extension to versions 1.8.7, 1.9.10, 2.0.5, 2.1.11, 2.2.9, or 2.3.7 respectively, which contain proper input validation and sanitization for URL parameters. System administrators should also implement proper input validation at multiple layers, including server-side sanitization of all URL parameters before they are processed or rendered in web pages. Additionally, the implementation of Content Security Policy headers can provide an additional defense layer by restricting script execution and preventing unauthorized code injection, though this should complement rather than replace proper input validation. Security monitoring should include detection of suspicious URL patterns and unexpected parameter handling within the WordPress environment, with particular attention to the add_query_arg function usage patterns in custom extensions. The vulnerability demonstrates the critical importance of proper input validation and output encoding in web applications, aligning with ATT&CK technique T1059.007 for script injection and T1566 for credential access through web application vulnerabilities. Organizations should also consider implementing web application firewalls to detect and block malicious payloads targeting similar XSS vulnerabilities in their WordPress installations.