CVE-2021-43558 in Moodle
Summary
by MITRE • 11/22/2021
A flaw was found in Moodle in versions 3.11 to 3.11.3, 3.10 to 3.10.7, 3.9 to 3.9.10 and earlier unsupported versions. A URL parameter in the filetype site administrator tool required extra sanitizing to prevent a reflected XSS risk.
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Analysis
by VulDB Data Team • 11/25/2021
This vulnerability resides within the Moodle learning management system where improper input validation occurs in the filetype site administrator tool. The flaw manifests when a malicious actor crafts a specially crafted URL containing reflective cross-site scripting payloads within the filetype parameter. This vulnerability affects multiple version streams including the 3.11.x series up to 3.11.3, 3.10.x series up to 3.10.7, 3.9.x series up to 3.9.10, and older unsupported releases. The vulnerability represents a classic reflected cross-site scripting issue that falls under CWE-79 which specifically addresses improper neutralization of input during web page generation in a web application. The root cause stems from insufficient sanitization of user-supplied input parameters before they are rendered back to the browser context, creating an attack surface where malicious scripts can be executed in the victim's browser session.
The operational impact of this vulnerability extends beyond simple data theft or session hijacking as it allows attackers to execute arbitrary JavaScript code within the context of authenticated administrators. When an administrator clicks on a maliciously crafted link containing the XSS payload, the script executes in their browser with full administrative privileges, potentially enabling complete system compromise. This risk is particularly severe given that the vulnerability exists in the site administrator tool which typically operates with elevated permissions. The attack vector follows standard XSS exploitation patterns where the malicious payload is reflected back to the user through the vulnerable parameter, making it difficult to detect and trace. This vulnerability directly maps to attack techniques described in the MITRE ATT&CK framework under T1059.001 for command and scripting interpreter and T1566.001 for spearphishing with a link, as it enables the delivery of malicious payloads through crafted web requests.
Mitigation strategies for this vulnerability require immediate patching of affected Moodle installations to versions that contain proper input sanitization for the filetype parameter. Organizations should implement comprehensive input validation and output encoding for all user-supplied parameters, particularly those used in administrative interfaces. The implementation of Content Security Policy headers can provide additional defense-in-depth measures to prevent execution of unauthorized scripts even if the primary vulnerability is exploited. Security teams should also conduct thorough audits of all web application parameters to identify similar input validation gaps, as this vulnerability demonstrates the importance of consistent sanitization practices across all application components. Regular security testing including dynamic application security testing and manual penetration testing should be performed to identify and remediate similar issues before they can be exploited by malicious actors. The vulnerability underscores the critical importance of maintaining up-to-date software versions and implementing robust security controls in educational technology platforms that handle sensitive user data and administrative functions.