CVE-2026-123655 in Moodle
Summary
by MITRE • 11/06/2026
A flaw was found in Moodle. Insufficient access control checks on H5P content files allow unauthenticated remote attackers to view restricted materials, including content stored in the system context and files belonging to hidden or unavailable course modules. This issue results in unauthorized information disclosure of protected content.
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Analysis
by VulDB Data Team • 11/06/2026
The vulnerability identified in Moodle represents a critical failure in access control mechanisms specifically affecting H5P interactive content files. As an experienced security specialist, it is evident that this flaw stems from insufficient validation of user permissions when serving static assets associated with H5P activities. The core technical issue lies in the web server or application layer's handling of file requests for these specific content types. When a request is made to access an H5P asset such as JavaScript, CSS, images, or media files, the system fails to adequately verify whether the requesting user has legitimate authorization to view the parent course module or context from which those assets originate. This architectural oversight allows unauthenticated remote attackers to bypass authentication and authorization checks entirely by directly targeting the file paths of these resources rather than interacting with the main application interface that typically enforces stricter security protocols.
This lack of proper access control results in a severe information disclosure vulnerability, classified under CWE-284 Improper Access Control. Attackers can exploit this flaw to retrieve sensitive materials stored within the system context or files belonging to course modules that are explicitly hidden from students or marked as unavailable for enrollment. In educational and corporate training environments using Moodle, such content often includes proprietary instructional materials, assessment questions with answers, internal communications, or other confidential data intended only for authorized participants. The ability of an unauthenticated actor to view these restricted resources undermines the fundamental confidentiality guarantees provided by the learning management system. This is not merely a theoretical risk but a practical vector for espionage and intellectual property theft within digital education platforms.
From an operational perspective, this vulnerability allows remote attackers to enumerate and access protected content without any prior authentication credentials. The impact extends beyond simple data leakage; it compromises the integrity of academic assessments by exposing exam questions or answer keys before they are administered. Furthermore, it erodes trust in the platform's security posture among administrators and users alike. The attack vector is particularly dangerous because it does not require social engineering or complex exploitation techniques involving client-side vulnerabilities. Instead, it relies on predictable file path structures common to H5P implementations, making automated scanning tools highly effective at identifying vulnerable instances across large networks of Moodle deployments.
To mitigate this risk, immediate remediation should focus on patching the underlying codebase to ensure that all requests for H5P assets are routed through proper authorization checks before being served. Administrators must verify that their instance is updated to a version where this access control logic has been corrected. In environments where upgrading is not immediately feasible, network-level controls such as web application firewalls can be configured to block direct access to known H5P asset directories unless accompanied by valid session tokens or authentication headers. Additionally, reviewing file permission settings and ensuring that the web server does not allow directory listing or direct execution of restricted files provides a layer of defense in depth. Continuous monitoring for unusual traffic patterns targeting these specific endpoints can also aid in early detection of exploitation attempts aligned with ATT&CK techniques related to unauthorized access to system resources.