CVE-2013-4939 in Moodle
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in io.swf in the IO Utility component in Yahoo! YUI 3.0.0 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-2013-4939 vulnerability represents a critical cross-site scripting flaw within the Yahoo! YUI 3.0.0 through 3.9.1 framework's IO Utility component, specifically affecting the io.swf module. This vulnerability manifests when the framework processes URLs containing crafted strings that are not properly sanitized before being rendered in web browsers. The issue impacts a wide range of software products including Moodle versions 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, and 2.5.x before 2.5.1, demonstrating the widespread adoption of this vulnerable component across various web applications. The vulnerability is categorized under CWE-79 as a failure to sanitize user input, specifically in the context of web script injection, making it a prime target for attackers seeking to exploit web application security weaknesses.
The technical flaw exists within the io.swf module's handling of URL parameters, where user-supplied data is directly incorporated into web page content without proper validation or sanitization. When a malicious user crafts a URL containing specially formatted strings, these inputs are processed by the vulnerable IO Utility component and subsequently executed within the browser context of legitimate users. This occurs because the framework fails to implement proper input filtering mechanisms that would normally escape or remove potentially dangerous characters from user-provided content. The vulnerability operates at the application layer and requires no special privileges to exploit, making it particularly dangerous as it can be triggered through simple web requests. The flaw aligns with ATT&CK technique T1059.007 for script injection and represents a classic case of insufficient input validation that allows attackers to bypass security controls.
The operational impact of this vulnerability extends beyond simple data theft or defacement, as it enables attackers to execute arbitrary JavaScript code within the context of authenticated users' browsers. This capability allows for session hijacking, credential theft, redirection to malicious sites, and potential privilege escalation within affected applications. When exploited in learning management systems like Moodle, attackers could gain access to student records, course materials, and administrative functions, compromising the integrity and confidentiality of educational data. The vulnerability's presence in multiple versions of popular web frameworks makes it particularly dangerous as organizations may have legacy systems that are difficult to patch or upgrade. Security researchers have noted that such vulnerabilities often remain undetected for extended periods due to the complexity of web application architectures and the difficulty in identifying all potential injection points within rich client-side frameworks.
Organizations affected by this vulnerability should implement immediate mitigations including applying the latest patches from Yahoo! YUI framework maintainers and Moodle developers, implementing proper input validation at all application layers, and deploying web application firewalls to detect and block malicious requests. The remediation process should include thorough code reviews to identify other potential injection points, implementation of Content Security Policy headers to limit script execution, and regular security testing to identify similar vulnerabilities. System administrators should also consider implementing monitoring solutions to detect anomalous behavior patterns that might indicate exploitation attempts, while security teams should develop incident response procedures specifically addressing XSS vulnerabilities. The vulnerability underscores the importance of maintaining up-to-date third-party components and implementing comprehensive security testing procedures that include both automated scanning and manual penetration testing to identify and remediate such critical flaws before they can be exploited by malicious actors.