CVE-2011-4588 in Moodle
Summary
by MITRE
The ip_in_range function in mnet/lib.php in MNET in Moodle 1.9.x before 1.9.15 uses an incorrect data type, which allows remote attackers to bypass intended IP address restrictions via an XMLRPC request.
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Analysis
by VulDB Data Team • 12/06/2021
The vulnerability described in CVE-2011-4588 resides within the MNET component of Moodle learning management system, specifically in the ip_in_range function located in mnet/lib.php. This flaw represents a critical security issue that affects Moodle versions 1.9.x prior to 1.9.15, where the improper handling of data types creates a pathway for malicious actors to circumvent IP address access controls. The vulnerability manifests through XMLRPC requests that exploit a type confusion error in the network communication layer, allowing unauthorized access to systems that should be restricted based on IP address ranges.
The technical root cause of this vulnerability stems from a data type mismatch within the ip_in_range function that processes IP address validation. When processing XMLRPC requests, the function fails to properly validate or convert the data types of IP address parameters, leading to a situation where attackers can manipulate the input to bypass access controls. This type confusion allows the system to interpret IP addresses incorrectly, effectively rendering the intended IP restriction mechanisms ineffective. The flaw operates at the network communication layer where MNET handles remote connections between Moodle instances, making it particularly dangerous as it can be exploited from external networks without requiring authentication.
The operational impact of this vulnerability is significant as it allows remote attackers to bypass IP-based access controls that are typically implemented to restrict access to Moodle instances from specific network ranges. This could enable unauthorized users to gain access to educational content, administrative functions, or sensitive data that should only be available to users within specific IP address ranges. The vulnerability affects the fundamental security model of Moodle installations that rely on IP restrictions for access control, potentially leading to data breaches, unauthorized modifications to course content, or full administrative access to vulnerable systems. Attackers could exploit this vulnerability to perform privilege escalation or gain unauthorized access to protected resources.
Mitigation strategies for this vulnerability require immediate patching of affected Moodle installations to version 1.9.15 or later, which contains the necessary fixes for the data type handling issue. Organizations should also implement additional network-level controls such as firewall rules to restrict access to XMLRPC endpoints and monitor network traffic for suspicious patterns. The fix addresses the underlying type confusion issue by ensuring proper data type validation and conversion within the ip_in_range function, preventing attackers from manipulating IP address parameters to bypass restrictions. Security teams should conduct comprehensive vulnerability assessments to identify any other instances of similar type confusion vulnerabilities within their Moodle installations and related systems. This vulnerability aligns with CWE-191, which describes integer underflow and underflow conditions, and represents a specific case of improper input validation that can be categorized under the ATT&CK technique T1190 for exploitation of remote services.
The broader implications of this vulnerability highlight the importance of proper input validation and type safety in network communication components. It demonstrates how seemingly minor implementation flaws in core functions can have significant security consequences, particularly in systems that rely on network-based access controls. Organizations should implement regular security testing of network communication components and maintain up-to-date security patches to prevent exploitation of similar vulnerabilities. The vulnerability also underscores the need for robust code review processes that focus on data type handling and input validation in security-critical functions.