CVE-2013-4941 in Moodle
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in uploader.swf in the Uploader component in Yahoo! YUI 3.2.0 through 3.9.1, as used in Moodle through 2.1.10, 2.2.x before 2.2.11, 2.3.x before 2.3.8, 2.4.x before 2.4.5, 2.5.x before 2.5.1, and other products, allows remote attackers to inject arbitrary web script or HTML via a crafted string in a URL.
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Analysis
by VulDB Data Team • 02/28/2019
The CVE-2013-4941 vulnerability represents a critical cross-site scripting flaw discovered in the Yahoo! YUI Uploader component version 3.2.0 through 3.9.1, which was extensively integrated into various web applications including Moodle versions up to 2.5.1. This vulnerability specifically affects the uploader.swf file, which is a flash-based file upload component that enables users to upload files to web servers through a graphical interface. The flaw stems from inadequate input validation and sanitization within the flash component's handling of URL parameters, creating an avenue for malicious actors to inject arbitrary web scripts or HTML content into the application's response.
The technical implementation of this vulnerability occurs when the uploader.swf component processes URL parameters without proper sanitization of user-supplied data. When a malicious user crafts a specially formatted URL containing script tags or HTML code within the parameters, the flash component fails to properly escape or validate these inputs before rendering them in the browser context. This allows attackers to execute arbitrary JavaScript code within the victim's browser session, potentially leading to session hijacking, data theft, or redirection to malicious websites. The vulnerability falls under CWE-79 which specifically addresses Cross-Site Scripting flaws, and can be categorized under ATT&CK technique T1566.001 for initial access through malicious web content.
The operational impact of this vulnerability extends beyond simple XSS attacks, as it can be leveraged to compromise entire user sessions and potentially escalate privileges within affected applications. In Moodle environments, where this component was widely used for file uploads, attackers could inject malicious scripts that would execute whenever legitimate users viewed the upload interface or accessed files uploaded through the vulnerable component. The vulnerability's widespread presence across multiple Moodle versions and other products demonstrates its significance as a common component flaw that affected numerous web applications relying on the YUI library. The attack vector is particularly dangerous because it requires minimal user interaction beyond visiting a maliciously crafted URL, making it an effective vector for social engineering campaigns.
Organizations affected by this vulnerability should implement immediate mitigation strategies including updating to patched versions of the YUI library and Moodle, implementing proper input validation at multiple layers, and deploying content security policies to prevent script execution. The recommended approach involves upgrading to YUI versions beyond 3.9.1 and Moodle versions that have incorporated security fixes, while also implementing proper parameter sanitization and output encoding techniques. Additionally, network administrators should consider implementing web application firewalls that can detect and block malicious URL patterns, and security teams should conduct comprehensive vulnerability assessments to identify any other instances of the vulnerable component within their application portfolios. The vulnerability serves as a reminder of the critical importance of validating all user inputs and the potential consequences of insufficient sanitization in web applications.