CVE-2015-9518 in PDF Invoices Extension
Summary
by MITRE
The Easy Digital Downloads (EDD) PDF Invoices 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-2015-9518 vulnerability affects the Easy Digital Downloads PDF Invoices extension for WordPress, representing a cross-site scripting flaw that emerged due to improper implementation of the add_query_arg function. This vulnerability specifically targets versions of EDD 1.8.x prior to 1.8.7, 1.9.x prior to 1.9.10, 2.0.x prior to 2.0.5, 2.1.x prior to 2.1.11, 2.2.x prior to 2.2.9, and 2.3.x prior to 2.3.7. The flaw stems from the extension's failure to properly sanitize or escape user-supplied input when constructing query arguments for URL generation, creating a pathway for malicious actors to inject arbitrary JavaScript code into web pages viewed by other users.
The technical exploitation of this vulnerability occurs when the PDF Invoices extension processes user input through the add_query_arg function without adequate sanitization measures. This function is designed to add or modify query parameters in URLs, but when misused in this context, it fails to properly escape output that contains unvalidated user data. The vulnerability manifests as a reflected cross-site scripting attack where an attacker can craft malicious URLs containing JavaScript payloads that get executed in the victim's browser when they view the PDF invoice. This misimplementation aligns with CWE-79, which categorizes cross-site scripting vulnerabilities as weaknesses in input validation and output encoding.
The operational impact of CVE-2015-9518 extends beyond simple script injection, as it provides attackers with the capability to execute arbitrary code within the context of a victim's browser session. This could enable session hijacking, credential theft, or redirection to malicious websites. Attackers could exploit this vulnerability by manipulating invoice generation parameters or by crafting specially crafted URLs that would be processed by the vulnerable extension. The attack vector is particularly concerning because it targets administrative interfaces where users might have elevated privileges, potentially allowing attackers to gain unauthorized access to sensitive financial data or administrative controls. This vulnerability falls under the ATT&CK technique T1566, specifically targeting credential access through phishing or malicious web content.
Organizations using vulnerable versions of the EDD PDF Invoices extension face significant security risks, particularly in environments where administrative users frequently generate or view PDF invoices. The vulnerability could be exploited by attackers who gain access to user sessions or by targeting specific administrative users through phishing campaigns. The remediation approach requires immediate patching of affected versions to EDD 1.8.7, 1.9.10, 2.0.5, 2.1.11, 2.2.9, or 2.3.7 respectively, which contain proper sanitization of query arguments. Additionally, implementing proper input validation and output escaping for all user-supplied data within URL generation functions is essential for preventing similar vulnerabilities. Security practitioners should also consider implementing web application firewalls and monitoring for suspicious URL patterns that might indicate exploitation attempts. The vulnerability demonstrates the critical importance of proper input sanitization and output encoding practices in web applications, particularly when dealing with URL construction and user interaction scenarios that could lead to XSS exploitation.