CVE-2018-1137 in Moodle
Summary
by MITRE
An issue was discovered in Moodle 3.x. By substituting URLs in portfolios, users can instantiate any class. This can also be exploited by users who are logged in as guests to create a DDoS attack.
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Analysis
by VulDB Data Team • 09/03/2025
The vulnerability identified as CVE-2018-1137 represents a critical security flaw within Moodle version 3.x that exposes the platform to unauthorized class instantiation through portfolio URL manipulation. This issue stems from insufficient input validation and access control mechanisms within the portfolio subsystem, allowing malicious actors to exploit the system's trust in user-provided URLs. The vulnerability specifically affects the portfolio functionality where users can specify external URLs to be processed, creating an attack surface that extends beyond typical user permissions.
The technical exploitation of this vulnerability involves manipulating portfolio URL parameters to trigger instantiation of arbitrary PHP classes within the Moodle environment. This occurs due to inadequate sanitization of user-supplied input that is subsequently used in object creation contexts. Attackers can leverage this flaw to execute unintended code sequences, potentially leading to remote code execution or privilege escalation within the application's execution context. The vulnerability is particularly dangerous because it operates through the portfolio subsystem, which is designed to facilitate content export and sharing between Moodle and external services, making it a legitimate entry point for exploitation.
The operational impact of CVE-2018-1137 extends beyond simple code execution to include potential denial of service scenarios, particularly when exploited by guest users who can leverage the vulnerability to launch distributed denial of service attacks. Guest accounts typically have limited permissions, but this vulnerability allows them to perform actions that would normally require authenticated administrative privileges. The DDoS capability arises from the ability to trigger resource-intensive operations through class instantiation, consuming server resources and potentially disrupting legitimate user access to the learning management system. This makes the vulnerability particularly concerning for organizations relying on Moodle for educational services where continuous availability is critical.
Security mitigations for this vulnerability should focus on implementing comprehensive input validation and sanitization of all portfolio URL parameters before processing. The recommended approach includes enforcing strict access controls that prevent unauthorized class instantiation and implementing proper object instantiation boundaries within the portfolio subsystem. Organizations should also consider implementing rate limiting mechanisms to prevent abuse of guest account capabilities and ensure that all user inputs are properly escaped before being processed. Additionally, regular security updates and patches should be applied immediately upon release to prevent exploitation, as this vulnerability has been documented and addressed in subsequent Moodle releases. The flaw aligns with CWE-772, which addresses insufficient resource management, and can be mapped to ATT&CK technique T1059 for remote code execution through command injection, highlighting the multi-faceted nature of the security threat.