CVE-2026-102585 in Moodle
Summary
by MITRE • 09/30/2026
A flaw was found in Moodle. When enrolling a user into a course while assigning them to a group, the application does not verify whether the selected group actually belongs to that course. An authenticated user with teacher privileges could exploit this flaw to add users to groups within courses they do not have authorization to access.
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Analysis
by VulDB Data Team • 09/30/2026
The vulnerability identified in Moodle represents a critical failure in server-side access control logic, specifically concerning the enforcement of scope boundaries during group enrollment operations. This issue stems from an insufficient verification mechanism where the application accepts user-supplied input for both course identifiers and group identifiers without establishing a valid relational link between them within the database context. In a properly secured system, when an administrator or teacher attempts to enroll a user into a specific group, the backend logic must query the database to confirm that the specified group ID is associated with the target course ID before proceeding with the enrollment transaction. The absence of this validation step creates a logical flaw where the application blindly trusts the provided parameters, allowing for arbitrary assignment of users to groups regardless of their actual membership in the targeted educational context.
From a technical perspective, this vulnerability falls under the category of Broken Access Control, which is consistently ranked as one of the most significant security risks by industry standards such as OWASP Top 10 and CWE-284 Improper Access Control. The specific nature of the flaw can also be classified under CWE-798: Use of Hard-coded Credentials or more accurately CWE-639: Authorization Bypass Through User-Controlled Key, depending on how the group ID is manipulated. By exploiting this lack of validation, an authenticated attacker with teacher privileges in one course can manipulate API endpoints or form submissions to target groups belonging to completely different courses. This bypasses the intended isolation mechanisms that separate distinct learning environments within a single Moodle instance, effectively allowing lateral movement across administrative boundaries without requiring elevated permissions for those specific targets.
The operational impact of this vulnerability is substantial, particularly in multi-tenant educational institutions where data privacy and strict role-based access control are paramount. An attacker can use this flaw to inject users into groups they do not have permission to view or manage. This could lead to unauthorized disclosure of sensitive information if the group contains private discussions, shared files, or graded assignments that should remain restricted to authorized participants. Furthermore, it enables potential disruption of academic activities by adding disruptive actors to active course groups, thereby compromising the integrity of collaborative learning environments. In severe cases, this flaw can serve as a stepping stone for further attacks, such as privilege escalation if subsequent actions rely on group membership status or if combined with other vulnerabilities like cross-site scripting within those unauthorized contexts.
Mitigation strategies must focus on implementing robust server-side validation checks that enforce strict referential integrity between courses and their associated groups. Developers should ensure that every enrollment request includes a verification step where the system queries the database to confirm that the group ID exists and is explicitly linked to the course ID provided in the same transaction. Additionally, adopting principle of least privilege by auditing teacher permissions can help limit exposure if such logical flaws exist elsewhere in the application. For immediate remediation without code changes, administrators should restrict access to enrollment APIs where possible and monitor logs for anomalous patterns indicating cross-course group manipulations. Long-term solutions involve integrating automated security testing into the development lifecycle to detect logic errors that traditional static analysis tools might miss, ensuring that all user inputs are validated against expected business rules before processing.