CVE-2015-3178 in Moodle
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in the external_format_text function in lib/externallib.php in Moodle through 2.5.9, 2.6.x before 2.6.11, 2.7.x before 2.7.8, and 2.8.x before 2.8.6 allows remote authenticated users to inject arbitrary web script or HTML into an external application via a crafted string that is visible to web services.
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Analysis
by VulDB Data Team • 05/19/2022
The CVE-2015-3178 vulnerability represents a critical cross-site scripting flaw discovered in the Moodle learning management system, affecting versions through 2.5.9, 2.6.x before 2.6.11, 2.7.x before 2.7.8, and 2.8.x before 2.8.6. This vulnerability resides within the external_format_text function located in the lib/externallib.php file, which serves as a core component for external web services within the Moodle platform. The flaw enables authenticated remote attackers to inject malicious web script or HTML code into external applications that utilize Moodle's web services, creating a significant security risk for organizations relying on this educational platform.
The technical implementation of this vulnerability stems from insufficient input validation and output sanitization within the external_format_text function. When Moodle processes external requests through its web services API, the function fails to properly escape or filter user-supplied input before rendering it in web contexts. This improper handling of user data creates an opening for attackers who can craft malicious strings containing embedded scripts or HTML tags that will execute in the context of other users' browsers. The vulnerability specifically impacts the external web services functionality, which allows third-party applications to interact with Moodle through standardized APIs, making the attack surface broader than typical XSS flaws.
The operational impact of CVE-2015-3178 extends beyond simple script injection, potentially enabling attackers to perform session hijacking, steal sensitive user information, redirect victims to malicious sites, or execute arbitrary commands within the context of authenticated user sessions. Given that Moodle is widely deployed in educational institutions, the compromise of a single authenticated user could potentially expose sensitive academic data, personal information, or institutional resources. The vulnerability affects the core web services infrastructure, meaning that any external application or integration relying on Moodle's API could become a vector for exploitation, amplifying the potential damage across interconnected systems.
Organizations can mitigate this vulnerability through several approaches aligned with industry best practices and standards. The primary remediation involves applying the official patches released by Moodle for the affected versions, which typically include proper input sanitization and output encoding mechanisms. Additionally, implementing proper web application firewall rules to detect and block suspicious script patterns in API requests can provide an additional layer of defense. According to CWE standards, this vulnerability maps to CWE-79 which specifically addresses Cross-site Scripting flaws, while the ATT&CK framework would categorize this under T1059.005 for Command and Scripting Interpreter and potentially T1566 for Phishing, as attackers could leverage this vulnerability to create malicious payloads that trick users into executing harmful code. Security teams should also consider implementing principle of least privilege for web service accounts and regularly audit external API integrations to identify potential exploitation vectors.