CVE-2011-4203 in Moodle
Summary
by MITRE
CRLF injection vulnerability in calendar/set.php in the Calendar component in Moodle 1.9.x before 1.9.15, 2.0.x before 2.0.6, 2.1.x before 2.1.3, and 2.2 allows remote attackers to inject arbitrary HTTP headers and conduct HTTP response splitting attacks via vectors involving the url variable.
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Analysis
by VulDB Data Team • 02/13/2019
The CVE-2011-4203 vulnerability represents a critical CRLF injection flaw within the Calendar component of Moodle learning management system. This vulnerability specifically affects versions 1.9.x prior to 1.9.15, 2.0.x prior to 2.0.6, and 2.1.x prior to 2.1.3, with the 2.2 branch also potentially impacted. The flaw exists in the calendar/set.php script which processes user input without proper sanitization, creating a pathway for malicious actors to manipulate HTTP headers through crafted input parameters.
The technical implementation of this vulnerability stems from insufficient input validation and sanitization within the url variable processing mechanism. When user-supplied data containing carriage return line feed sequences is directly incorporated into HTTP response headers without proper encoding or filtering, attackers can inject additional HTTP headers into the server's response. This CRLF injection allows for HTTP response splitting attacks where malicious content can be injected between the HTTP headers and the response body, potentially enabling session hijacking, cross-site scripting attacks, or cache poisoning techniques.
The operational impact of this vulnerability extends beyond simple header injection, as it provides attackers with the capability to manipulate web server responses in ways that can compromise user sessions and data integrity. By leveraging HTTP response splitting, attackers could potentially redirect users to malicious websites, inject malicious content into responses, or manipulate browser behavior through crafted HTTP headers. The vulnerability affects the core calendar functionality of Moodle, which is extensively used by educational institutions for scheduling and event management, making it an attractive target for exploitation.
Security practitioners should note that this vulnerability aligns with CWE-113, which specifically addresses improper neutralization of CRLF characters in HTTP headers, and maps to ATT&CK technique T1190 for exploiting vulnerabilities in web applications. The risk is particularly elevated in environments where Moodle serves as a central authentication or information repository, as successful exploitation could lead to broader system compromise. Organizations should immediately apply the available patches for affected versions and implement proper input validation measures to prevent similar vulnerabilities in other components of their web applications.
Mitigation strategies should include immediate patch deployment for all affected Moodle versions, implementation of strict input validation for all user-supplied parameters, and regular security assessments of web application components. Additionally, organizations should consider implementing web application firewalls and monitoring for suspicious HTTP header patterns to detect potential exploitation attempts. The vulnerability serves as a reminder of the critical importance of proper input sanitization in web applications and the potential consequences of failing to address CRLF injection vulnerabilities in server-side components that handle user input.