CVE-2013-4942 in Moodle
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in flashuploader.swf in the Uploader component in Yahoo! YUI 3.5.0 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-2013-4942 vulnerability represents a critical cross-site scripting flaw located within the flashuploader.swf component of Yahoo! YUI 3.5.0 through 3.9.1 library versions. This vulnerability specifically affects the Uploader component's flash-based file upload functionality and has been identified in Moodle versions up to 2.1.10, 2.2.x through 2.2.10, 2.3.x through 2.3.7, 2.4.x through 2.4.4, and 2.5.x through 2.5.0, along with numerous other products that utilize this library. The flaw stems from insufficient input validation and sanitization within the flash-based uploader, creating a pathway for malicious actors to execute arbitrary web scripts or HTML code in the context of affected applications.
The technical implementation of this vulnerability occurs when the flashuploader.swf component processes user-supplied input through URL parameters without proper sanitization mechanisms. When a malicious user crafts a specially crafted string and injects it into a URL parameter that gets processed by the flash component, the vulnerable code fails to properly escape or validate the input before rendering it within the web page context. This allows attackers to inject malicious scripts that execute in the victim's browser session, potentially leading to session hijacking, data theft, or further exploitation of the vulnerable system. The vulnerability operates at the client-side execution layer where flash content interacts with web page elements, making it particularly dangerous as it can bypass traditional server-side security controls.
The operational impact of CVE-2013-4942 extends beyond simple script injection, as it creates a persistent vector for attackers to compromise user sessions and potentially escalate privileges within affected applications. In Moodle environments, this vulnerability could enable attackers to gain unauthorized access to user accounts, modify course content, access sensitive educational data, or even establish persistent backdoors within learning management systems. The widespread adoption of YUI library components across various web applications means that this vulnerability affects not just Moodle installations but numerous other platforms that integrate the affected library versions. Attackers can leverage this vulnerability to perform session fixation attacks, steal authentication tokens, or redirect users to malicious sites, making it a significant threat to user privacy and system integrity.
Organizations should implement immediate mitigations including updating to patched versions of YUI library components, specifically upgrading to versions beyond 3.9.1, and applying corresponding Moodle security patches that address this vulnerability. Input validation should be strengthened at both client and server levels, with proper HTML escaping and sanitization routines implemented to prevent malicious code execution. Network-based mitigations such as web application firewalls can provide additional protection layers, though they should not replace proper code-level fixes. Security monitoring should be enhanced to detect suspicious URL patterns and unusual file upload activities that might indicate exploitation attempts. The vulnerability aligns with CWE-79 which specifically addresses cross-site scripting flaws, and represents a clear violation of secure coding practices for input validation and output encoding. From an ATT&CK framework perspective, this vulnerability maps to techniques involving code injection and credential access, with potential for privilege escalation and persistence within affected systems. Organizations must conduct thorough vulnerability assessments to identify all instances of the vulnerable YUI library versions and ensure complete remediation across their entire application ecosystem.