CVE-2013-4523 in Moodle
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in message/lib.php in Moodle through 2.2.11, 2.3.x before 2.3.10, 2.4.x before 2.4.7, and 2.5.x before 2.5.3 allows remote authenticated users to inject arbitrary web script or HTML via a crafted message.
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Analysis
by VulDB Data Team • 06/15/2017
The CVE-2013-4523 vulnerability represents a critical cross-site scripting flaw discovered in Moodle's message library component, affecting multiple versions of the popular learning management system. This vulnerability exists within the message/lib.php file and specifically targets the handling of user-supplied message content without proper sanitization or validation. The flaw allows authenticated users to inject malicious web scripts or HTML code into message systems, creating a persistent security risk that can affect all users within the Moodle environment. The vulnerability's impact extends beyond simple data theft as it enables attackers to execute arbitrary code in the context of other users' browsers, potentially leading to complete account compromise and unauthorized access to sensitive educational data.
The technical implementation of this vulnerability stems from insufficient input validation and output encoding within Moodle's messaging infrastructure. When authenticated users send messages containing malicious payloads, the system fails to properly sanitize the content before storing or displaying it. This weakness aligns with CWE-79, which specifically addresses cross-site scripting vulnerabilities where untrusted data is improperly integrated into web pages. The flaw operates through the standard message passing mechanism within Moodle, making it particularly dangerous as legitimate users are often unaware they are processing malicious content. The vulnerability requires authentication to exploit, but once compromised, attackers can leverage the authenticated session to inject scripts that execute in the context of other users' browsers, potentially enabling session hijacking, data exfiltration, and privilege escalation.
The operational impact of CVE-2013-4523 extends significantly beyond immediate script execution capabilities, as it creates persistent attack vectors that can compromise entire Moodle instances. Attackers can craft malicious messages containing JavaScript payloads that execute when other users read the messages, potentially stealing session cookies, redirecting users to phishing sites, or modifying course content. This vulnerability particularly affects educational institutions relying on Moodle for their learning management needs, as it can lead to unauthorized access to student records, course materials, and administrative functions. The attack surface is broad given that Moodle's messaging system is integral to communication between students, instructors, and administrators, making every message exchange a potential attack point. The vulnerability also aligns with ATT&CK technique T1059.007, which covers scripting through web shells, as malicious code can be injected and executed through the message system.
Mitigation strategies for CVE-2013-4523 focus primarily on immediate version upgrades to patched releases of Moodle, specifically targeting versions 2.2.11, 2.3.10, 2.4.7, and 2.5.3 where the vulnerability has been addressed. Organizations should implement comprehensive input validation and output encoding measures within their Moodle installations, ensuring that all user-generated content undergoes strict sanitization before storage or display. Network-level protections such as web application firewalls and content filtering systems can provide additional defense in depth, though these should not replace proper application-level fixes. Security monitoring should include detection of suspicious message content patterns and anomalous user behavior that might indicate exploitation attempts. Regular security audits and penetration testing of Moodle installations are essential to identify similar vulnerabilities and maintain robust security postures. The remediation process should also include user education about recognizing potentially malicious messages and implementing proper access controls to limit message injection capabilities where possible.