CVE-2019-14827 in Moodle
Summary
by MITRE • 05/17/2021
A vulnerability was found in Moodle where javaScript injection was possible in some Mustache templates via recursive rendering from contexts. Mustache helper tags that were included in template contexts were not being escaped before that context was injected into another Mustache helper, which could result in script injection in some templates. This affects versions 3.7 to 3.7.1, 3.6 to 3.6.5, 3.5 to 3.5.7 and earlier unsupported versions.
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Analysis
by VulDB Data Team • 05/22/2021
This vulnerability in Moodle represents a critical server-side template injection flaw that exploits the recursive rendering mechanism of Mustache templates. The issue arises when JavaScript code is embedded within Mustache helper tags that are subsequently processed through recursive template rendering operations. The root cause lies in insufficient input sanitization and output escaping of template contexts, creating a pathway for malicious code execution. Attackers can leverage this weakness to inject arbitrary JavaScript into vulnerable templates, potentially compromising user sessions and system integrity. The vulnerability affects multiple major release versions including 3.7.0-3.7.1, 3.6.0-3.6.5, and 3.5.0-3.5.7, with older unsupported versions also being susceptible to exploitation.
The technical implementation of this vulnerability stems from improper handling of context data within the Mustache template engine integration. When Mustache helper tags contain unescaped user-provided data from template contexts, the recursive rendering process fails to properly sanitize this information before injecting it into subsequent template operations. This creates a chain reaction where malicious payloads can propagate through the template system and execute within the browser context of affected users. The flaw specifically targets the template processing pipeline where context variables are passed between different Mustache helper operations without adequate security measures. According to CWE-79, this represents a classic cross-site scripting vulnerability that occurs during dynamic code generation, making it particularly dangerous in educational platform environments where users may have varying privilege levels.
The operational impact of this vulnerability extends beyond simple script injection, potentially enabling attackers to perform session hijacking, data exfiltration, and privilege escalation within the Moodle environment. Users with higher privileges could be targeted to gain administrative access, while regular users might experience unauthorized actions such as content modification or account takeovers. The recursive nature of the vulnerability means that a single malicious input can propagate through multiple template layers, amplifying the potential damage. Organizations using affected Moodle versions face significant security risks, particularly in environments with numerous users, as the attack surface increases with user interaction volume. The vulnerability can be exploited through various vectors including course content creation, user profile modifications, or any template-based user input fields.
Mitigation strategies should focus on immediate patch application to the affected Moodle versions, with security updates addressing the template escaping mechanism and implementing proper input validation for Mustache contexts. Organizations should also consider implementing web application firewalls to detect and block suspicious template injection attempts, along with comprehensive monitoring of template-related user activities. Regular security audits should examine all template processing pathways and ensure proper escaping mechanisms are in place for all user-provided content. According to ATT&CK framework, this vulnerability maps to T1059.007 for script injection techniques and T1566 for social engineering through template manipulation. Additional defensive measures include restricting user permissions for template modifications, implementing content security policies, and establishing automated scanning for potentially malicious template content. The vulnerability highlights the critical importance of secure template processing in web applications and underscores the need for comprehensive security testing of rendering engines in educational platforms.