CVE-2011-4302 in Moodle
Summary
by MITRE
mnet/xmlrpc/client.php in MNET in Moodle 1.9.x before 1.9.14, 2.0.x before 2.0.5, and 2.1.x before 2.1.2 does not properly process the return value of the openssl_verify function, which allows remote attackers to bypass validation via a crafted certificate.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 12/05/2021
The vulnerability described in CVE-2011-4302 affects the Moodle network authentication system known as MNET which is used for federated authentication between Moodle installations. This flaw exists in multiple versions of Moodle including 1.9.x before 1.9.14, 2.0.x before 2.0.5, and 2.1.x before 2.1.2, representing a critical security weakness in the certificate validation process. The issue stems from improper handling of the openssl_verify function return value within the mnet/xmlrpc/client.php file, which creates a pathway for malicious actors to circumvent the intended security controls.
The technical flaw manifests when the system fails to properly validate the return code from the openssl_verify function, which is responsible for confirming the authenticity of SSL certificates used in secure communications. This function returns a value indicating whether the certificate verification was successful, but the MNET implementation does not correctly interpret this return value. When a crafted certificate is presented, the system incorrectly processes the verification result, allowing untrusted certificates to be accepted as valid. This represents a classic case of improper input validation and error handling, which aligns with CWE-252, or "Unchecked Return Value" in the Common Weakness Enumeration catalog.
The operational impact of this vulnerability is significant as it enables remote attackers to perform man-in-the-middle attacks against Moodle installations using the MNET functionality. Attackers can craft malicious certificates that bypass the certificate validation process, potentially allowing them to impersonate legitimate Moodle servers or intercept communications between Moodle instances. This compromise undermines the fundamental security assumptions of the SSL/TLS protocol and can lead to unauthorized access to sensitive educational data, user credentials, and institutional information. The vulnerability particularly affects organizations that rely on federated authentication between Moodle instances, making it a serious concern for educational institutions and learning management system administrators.
The exploitation of this vulnerability aligns with techniques described in the MITRE ATT&CK framework under the "Credential Access" and "Initial Access" domains, where attackers can leverage weakened authentication mechanisms to gain unauthorized access to systems. Organizations using affected Moodle versions should immediately implement the available patches released by Moodle developers, which properly handle the openssl_verify return values and ensure that certificate validation failures are correctly processed. Additional mitigations include implementing network-level monitoring to detect suspicious certificate exchanges and considering the temporary disabling of MNET functionality until proper updates can be deployed across all affected systems. This vulnerability demonstrates the critical importance of proper cryptographic implementation and validation in security-sensitive applications, particularly those handling educational data and user authentication.