CVE-2011-4586 in Moodle
Summary
by MITRE
CRLF injection vulnerability in calendar/set.php in the Calendar subsystem in Moodle 1.9.x before 1.9.15, 2.0.x before 2.0.6, and 2.1.x before 2.1.3 allows remote attackers to inject arbitrary HTTP headers and conduct HTTP response splitting attacks via unspecified vectors.
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Analysis
by VulDB Data Team • 12/06/2021
The CVE-2011-4586 vulnerability represents a critical CRLF injection flaw within Moodle's calendar subsystem that enables remote attackers to manipulate HTTP headers and execute response splitting attacks. This vulnerability specifically affects Moodle 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, making it a widespread issue across multiple major release branches. The vulnerability resides in the calendar/set.php file, which processes calendar-related operations and fails to properly sanitize user input before incorporating it into HTTP response headers. This flaw falls under CWE-113, which specifically addresses improper neutralization of CRLF sequences in HTTP headers, making it a direct descendant of the well-known HTTP response splitting vulnerability pattern. The attack vector involves injecting carriage return line feed sequences into HTTP headers, allowing adversaries to inject malicious content that can be interpreted by web browsers as separate HTTP responses.
The technical exploitation of this vulnerability enables attackers to manipulate the HTTP response stream by injecting CRLF sequences that separate the original HTTP headers from subsequent malicious headers. When user-provided data flows into the calendar subsystem without proper sanitization, attackers can craft inputs that contain characters such as \r or \n which are interpreted as CRLF sequences. This creates a condition where the web server appends additional headers or content to the HTTP response, potentially allowing for session hijacking, cross-site scripting attacks, or cache poisoning. The vulnerability is particularly dangerous in web applications where users can influence data that gets written to HTTP headers, as it bypasses normal input validation mechanisms and can be leveraged to manipulate the application's response behavior. The calendar subsystem in Moodle typically handles user events, scheduling, and notification systems, making it an attractive target for attackers seeking to inject malicious content into HTTP responses.
The operational impact of CVE-2011-4586 extends beyond simple header injection, as it provides attackers with the capability to conduct sophisticated HTTP response splitting attacks that can compromise user sessions and data integrity. When exploited successfully, this vulnerability allows attackers to inject arbitrary HTTP headers that can redirect users to malicious sites, inject JavaScript code, or manipulate cookies and authentication tokens. The calendar functionality in Moodle is often used for user notifications, event scheduling, and collaborative work, making it a high-value target for attackers seeking to compromise user accounts or manipulate calendar data. The vulnerability's presence in multiple Moodle versions indicates that it was a persistent issue that required patches across different release branches, highlighting the severity and widespread nature of the problem. From an ATT&CK framework perspective, this vulnerability maps to T1566 (Phishing) and T1071.004 (Application Layer Protocol: DNS) as attackers can use the header injection to redirect users or manipulate DNS responses through HTTP headers.
Organizations using affected Moodle versions should prioritize immediate patching to remediate this vulnerability, as the attack surface is broad and the potential for exploitation is significant. The fix typically involves implementing proper input validation and sanitization of user data before it is incorporated into HTTP headers, ensuring that CRLF sequences are properly escaped or removed from user inputs. Security teams should also implement network monitoring to detect potential exploitation attempts, particularly around calendar-related functionality and HTTP header manipulation patterns. The vulnerability demonstrates the importance of input validation in web applications, especially in components that interact with HTTP protocols and headers. Additionally, organizations should review their web application firewall rules to detect and block CRLF injection attempts, and implement proper security headers to mitigate the impact of potential exploitation. Regular security assessments and code reviews focusing on HTTP header handling and input sanitization should be conducted to prevent similar vulnerabilities from emerging in other components of the Moodle platform or related applications.