CVE-2015-5332 in Moodle
Summary
by MITRE
Atto in Moodle 2.8.x before 2.8.9 and 2.9.x before 2.9.3 allows remote attackers to cause a denial of service (disk consumption) by leveraging the guest role and entering drafts with the editor-autosave feature.
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Analysis
by VulDB Data Team • 07/08/2022
The vulnerability identified as CVE-2015-5332 affects the Atto text editor component within Moodle learning management systems version 2.8.x before 2.8.9 and 2.9.x before 2.9.3. This issue represents a significant security flaw that enables remote attackers to consume excessive disk space through a specific exploitation vector involving the guest user role and the editor-autosave functionality. The vulnerability falls under the category of resource exhaustion attacks and demonstrates a critical weakness in the system's input validation and resource management mechanisms.
The technical flaw manifests through the editor-autosave feature which continuously saves user input to draft storage areas without proper size limitations or validation checks. When guest users exploit this functionality, they can repeatedly submit content that accumulates in the system's draft areas, leading to rapid disk space consumption. The vulnerability specifically targets the guest role permissions which, despite being restricted, still allow sufficient access to trigger this autosave mechanism. This behavior creates a persistent resource drain that can ultimately lead to system instability and complete denial of service conditions. The flaw operates at the application layer and does not require authentication beyond guest access, making it particularly dangerous as it can be exploited by anyone with basic system access.
The operational impact of this vulnerability extends beyond simple disk space consumption to encompass broader system stability and availability concerns. Attackers can systematically fill storage volumes with autosaved drafts, potentially causing the entire Moodle system to become unavailable for legitimate users. This resource exhaustion attack can lead to database corruption, application crashes, and complete system downtime. The vulnerability affects organizations that rely on Moodle for educational content management and can result in significant operational disruption. Additionally, the persistent nature of the attack means that even after initial exploitation, the system remains vulnerable until the affected drafts are manually cleared or the system is patched.
Security mitigations for CVE-2015-5332 should focus on immediate patch application to the affected Moodle versions, as well as implementing additional monitoring and resource limits. Organizations should establish automated alerts for disk space usage and implement rate limiting on autosave operations. The fix typically involves modifying the editor-autosave functionality to enforce size limits on draft content and implement proper cleanup procedures. This vulnerability aligns with CWE-400, which addresses excessive resource consumption, and can be mapped to ATT&CK technique T1499.001 for resource exhaustion attacks. System administrators should also consider implementing network-level controls to monitor for unusual autosave activity and establish regular maintenance procedures to clean draft storage areas. The incident highlights the importance of proper input validation and resource management in web applications, particularly those serving guest users with limited but still potentially harmful access privileges.