CVE-2011-4305 in Moodle
Summary
by MITRE
message/refresh.php in Moodle 1.9.x before 1.9.14 allows remote authenticated users to cause a denial of service (infinite request loop) via a URL that specifies a zero wait time for message refreshing.
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Analysis
by VulDB Data Team • 12/05/2021
The vulnerability identified as CVE-2011-4305 affects Moodle version 1.9.x prior to 1.9.14 and resides within the message/refresh.php component of the learning management system. This issue represents a classic denial of service vulnerability that can be exploited by authenticated users to disrupt normal system operations. The flaw specifically manifests when a user crafts a malicious URL that sets the message refreshing wait time to zero, creating an infinite loop condition that consumes system resources and prevents legitimate users from accessing messaging functionality.
The technical implementation of this vulnerability stems from inadequate input validation and sanitization within the message refreshing mechanism. When a user with valid credentials accesses the message/refresh.php script with a zero wait time parameter, the system fails to properly validate this input value. This allows the application to enter an infinite loop where it continuously refreshes messages without any delay, effectively consuming cpu cycles and memory resources. The vulnerability operates at the application layer and requires only authenticated access, making it particularly concerning as it can be exploited by users who have legitimate system access but malicious intent.
From an operational impact perspective, this vulnerability creates significant disruption to Moodle's messaging service and can potentially affect the entire learning platform. The infinite request loop consumes server resources such as cpu time, memory allocation, and network bandwidth, which can lead to system slowdowns or complete service unavailability. In environments where Moodle is used for large-scale educational institutions or corporate training, this denial of service condition can severely impact user experience and educational or business continuity. The vulnerability also represents a potential vector for resource exhaustion attacks that could be amplified if multiple users exploit the flaw simultaneously.
The vulnerability aligns with CWE-400, which categorizes it as an unchecked input validation issue where the system fails to properly validate user-provided parameters before processing them. From an attack perspective, this vulnerability maps to the denial of service category within the MITRE ATT&CK framework, specifically under the technique of resource exhaustion. The exploitation requires minimal technical skill as it only necessitates crafting a specific URL with a zero value parameter, making it accessible to attackers with basic knowledge of web application behavior. Organizations should implement input validation controls to prevent zero or negative values from being processed by the message refreshing component, and should also consider implementing rate limiting mechanisms to prevent abuse of the messaging system. The recommended remediation involves applying the official Moodle patch that was released as part of version 1.9.14, which includes proper validation of the wait time parameter to prevent invalid values from triggering the problematic loop condition.