CVE-2021-43687 in chamilo-lms
Summary
by MITRE • 12/01/2021
chamilo-lms v1.11.14 is affected by a Cross Site Scripting (XSS) vulnerability in /plugin/jcapture/applet.php if an attacker passes a message hex2bin in the cookie.
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Analysis
by VulDB Data Team • 12/08/2021
The vulnerability identified as CVE-2021-43687 affects Chamilo Learning Management System version 1.11.14 and represents a cross site scripting flaw that resides within the plugin/jcapture/applet.php component. This security weakness manifests when the application processes a message parameter that has been hex2bin encoded within the cookie structure, creating an avenue for malicious code execution. The vulnerability stems from inadequate input validation and sanitization mechanisms that fail to properly handle encoded data passed through HTTP cookies.
The technical implementation of this XSS vulnerability occurs through the processing of hex2bin encoded data within the cookie parameter, which is then improperly rendered in the web application's output without adequate sanitization. When an attacker crafts a malicious cookie containing hex2bin encoded JavaScript code, the application decodes this content and subsequently executes it within the context of a victim's browser session. This flaw operates under CWE-79 which categorizes cross site scripting vulnerabilities as weaknesses that allow attackers to inject malicious scripts into web applications viewed by other users. The vulnerability specifically targets the cookie handling mechanism and demonstrates a classic case of improper input validation where encoded content bypasses security checks.
The operational impact of this vulnerability extends beyond simple script execution as it provides attackers with the capability to hijack user sessions, steal sensitive information, and potentially escalate privileges within the learning management system. An attacker could craft malicious payloads that redirect users to phishing sites, steal authentication cookies, or manipulate the application's behavior to gain unauthorized access to course materials and user data. The vulnerability affects the confidentiality, integrity, and availability of the system by enabling unauthorized access to sensitive user information and potentially compromising the entire learning environment. This flaw particularly impacts educational institutions that rely on Chamilo LMS for their online learning platforms, as it creates persistent security risks for both administrators and students.
Mitigation strategies for CVE-2021-43687 should prioritize immediate patching of the Chamilo LMS application to version 1.11.15 or later, which contains the necessary fixes for this vulnerability. Organizations should implement comprehensive input validation and sanitization measures that properly decode and validate all cookie content before processing, ensuring that hex2bin encoded data undergoes strict validation. Network security controls including web application firewalls and intrusion prevention systems should be configured to monitor for suspicious cookie patterns and block known malicious payloads. Additionally, security teams should conduct regular vulnerability assessments and implement proper cookie security headers including HttpOnly and Secure flags to minimize the impact of successful XSS attacks. The remediation process should also include user education regarding the risks of clicking suspicious links and the importance of maintaining updated software versions. This vulnerability aligns with ATT&CK technique T1059.007 which covers script-based execution through web shells and malicious scripts, emphasizing the need for robust input validation and output encoding practices across all web application components.