CVE-2026-30884
Published: 18 March 2026
Summary
CVE-2026-30884 is a critical-severity Authorization Bypass Through User-Controlled Key (CWE-639) vulnerability. Its CVSS base score is 9.6 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 5.8th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 AC-3 (Access Enforcement) and AC-6 (Least Privilege).
Threat & Defense at a Glance
Threat & Defense Details
Mitigating Controls (NIST 800-53 r5)AI
Enforces approved authorizations by verifying that the supplied elementid belongs to the teacher's authorized course context, directly preventing cross-course information disclosure and data tampering.
Applies least privilege to restrict mod/customcert:manage capability strictly to the specific course context, mitigating unauthorized access to elements in other courses.
Validates the elementid input parameter in the editelement callback and mod_customcert_save_element web service against the authorized context, blocking invalid cross-course operations.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Authorization bypass (IDOR) in public-facing Moodle web services directly enables exploitation of T1190 for initial access, T1213 for unauthorized cross-course data retrieval from certificate repositories, and T1565.001 for tampering with stored certificate elements.
NVD Description
mdjnelson/moodle-mod_customcert is a Moodle plugin for creating dynamically generated certificates with complete customization via the web browser. Prior to versions 4.4.9 and 5.0.3, a teacher who holds `mod/customcert:manage` in any single course can read and silently overwrite certificate elements belonging…
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to any other course in the Moodle installation. The `core_get_fragment` callback `editelement` and the `mod_customcert_save_element` web service both fail to verify that the supplied `elementid` belongs to the authorized context, enabling cross-course information disclosure and data tampering. Versions 4.4.9 and 5.0.3 fix the issue.
Deeper analysisAI
CVE-2026-30884 is a vulnerability in the mdjnelson/moodle-mod_customcert Moodle plugin, which enables dynamically generated certificates with web-based customization. In versions prior to 4.4.9 and 5.0.3, the core_get_fragment callback editelement and the mod_customcert_save_element web service fail to verify that the supplied elementid belongs to the authorized course context. This authorization bypass, tied to CWE-639, allows cross-course access to certificate elements and carries a CVSS v3.1 score of 9.6 (AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N).
An authenticated teacher with the mod/customcert:manage capability in any single course can exploit this remotely without user interaction. They can read sensitive certificate elements from other courses, disclosing confidential information, and silently overwrite those elements, tampering with data across the Moodle installation.
The vulnerability is addressed in plugin versions 4.4.9 and 5.0.3. Additional mitigation details appear in the GitHub security advisory at GHSA-8pjr-j7r4-ccjx, along with the fixing commits a1494a80fb953f187f7888a7394cbf9d13c28468 and ddc8f01f1e19fb61202f6013a38ef757486d3ba0.
Details
- CWE(s)