CVE-2021-20183 in Moodle
Summary
by MITRE • 01/29/2021
It was found in Moodle before version 3.10.1 that some search inputs were vulnerable to reflected XSS due to insufficient escaping of search queries.
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Analysis
by VulDB Data Team • 02/21/2021
This vulnerability exists in Moodle versions prior to 3.10.1 where search functionality fails to properly sanitize user input, creating a reflected cross-site scripting vulnerability. The flaw occurs when users submit search queries that contain malicious script code which gets reflected back to the browser without adequate output encoding. This type of vulnerability falls under CWE-79 - Improper Neutralization of Input During Web Page Generation, which is a fundamental web application security weakness that allows attackers to inject malicious scripts into web pages viewed by other users.
The technical implementation of this vulnerability stems from insufficient input validation and output encoding practices within Moodle's search module. When search parameters are processed and displayed in the user interface, the application does not properly escape special characters that could be interpreted as HTML or JavaScript code. Attackers can exploit this by crafting search queries containing malicious payloads such as javascript:alert(1) or other script tags that execute in the context of other users' browsers. The reflected nature of this vulnerability means that the malicious script is immediately reflected from the web server back to the client without being stored, making it particularly dangerous for session hijacking and credential theft attacks.
The operational impact of this vulnerability extends beyond simple script execution as it can enable attackers to perform various malicious activities including session hijacking, credential theft, and redirection to malicious websites. An attacker who successfully exploits this vulnerability can manipulate the search functionality to inject scripts that capture user credentials, steal session cookies, or redirect users to phishing sites. This vulnerability particularly affects organizations that rely heavily on Moodle's search capabilities and have users who might unknowingly trigger the malicious payloads through search queries. The vulnerability is categorized under ATT&CK technique T1531 - Account Access Removal, as it can be used to compromise user sessions and gain unauthorized access to sensitive educational data.
Organizations should immediately upgrade to Moodle version 3.10.1 or later where this vulnerability has been patched through proper input sanitization and output encoding mechanisms. The fix typically involves implementing comprehensive HTML escaping of search query parameters before displaying them in web pages, ensuring that all user-supplied input undergoes proper validation and encoding before being rendered in the browser context. Additional mitigations include implementing web application firewalls to detect and block suspicious search patterns, monitoring search logs for unusual query patterns, and conducting regular security assessments of web applications to identify similar input validation weaknesses. Security teams should also consider implementing content security policies to further protect against XSS attacks and ensure that user input is properly validated at multiple layers of the application stack.