CVE-2013-4940 in Moodle
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in io.swf in the IO Utility component in Yahoo! YUI 3.10.2, 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. NOTE: this vulnerability exists because of a CVE-2013-4939 regression.
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Analysis
by VulDB Data Team • 02/28/2019
The vulnerability described in CVE-2013-4940 represents a cross-site scripting flaw within the IO Utility component of Yahoo! YUI framework version 3.10.2, specifically affecting the io.swf module. This issue manifests as a security weakness that enables remote attackers to execute malicious web scripts or HTML content through manipulated URL parameters. The vulnerability was particularly significant because it affected multiple versions of Moodle, spanning from 2.1.10 down to 2.5.1, as well as other products utilizing the affected YUI library components. The presence of this flaw in widely used educational platforms and web applications created substantial risk for organizations relying on these systems.
The technical root cause of this vulnerability stems from insufficient input validation and sanitization within the io.swf module of the YUI library. When processing URL parameters containing crafted strings, the system fails to properly escape or filter user-supplied data before incorporating it into web page content. This regression was introduced as a consequence of CVE-2013-4939, indicating that security improvements or fixes in previous versions inadvertently created this new attack vector. The flaw operates by allowing malicious input to bypass security controls that should prevent script execution in web contexts, effectively creating an injection point for arbitrary code execution within the victim's browser environment.
The operational impact of CVE-2013-4940 extends beyond simple data theft or defacement, as it provides attackers with the capability to manipulate user sessions, redirect victims to malicious sites, or harvest sensitive information from authenticated users. Given that Moodle platforms often contain educational data, student records, and administrative information, successful exploitation could lead to unauthorized access to confidential academic records, grade modifications, or complete system compromise. The vulnerability affects not only the targeted Moodle installations but also any other software products that integrate the affected YUI 3.10.2 library, creating a widespread attack surface that security teams must address across multiple systems.
Organizations affected by this vulnerability should implement immediate mitigations including updating to patched versions of Moodle and the YUI library, applying input validation controls at the application level, and implementing content security policies to restrict script execution. The vulnerability aligns with CWE-79, which classifies cross-site scripting as a critical weakness in web applications, and maps to ATT&CK technique T1059.007 for script injection. Security measures should include regular security assessments of third-party components, implementation of web application firewalls, and comprehensive testing of input handling mechanisms to prevent similar regressions in future updates. Additionally, administrators should monitor for any related vulnerabilities that may emerge from the same codebase or library components to ensure comprehensive protection against evolving threats.