CVE-2025-3636 is a medium-severity authorization bypass vulnerability identified in multiple recent versions of Moodle, specifically versions 4.1.0, 4.3.0, 4.4.0, and 4.5.0. Moodle is a widely used open-source learning management system (LMS) that facilitates online education and training. The vulnerability arises due to insufficient capability checks when accessing RSS feeds, allowing unauthorized users to bypass normal authorization controls. Specifically, the flaw involves a user-controlled key that can be manipulated to gain access to RSS feed content that should otherwise be restricted. This means that an attacker without proper permissions can view potentially sensitive information disseminated through these feeds. Although the vulnerability does not appear to require authentication or user interaction, it affects the confidentiality of information by exposing data intended only for authorized users. The lack of known exploits in the wild suggests that active exploitation has not yet been observed, but the presence of this flaw in widely deployed versions of Moodle makes it a notable risk. The vulnerability was reserved and published in April 2025, and while no official patches or vendor advisories are linked in the provided information, it is expected that Moodle maintainers will address this issue promptly given its nature. The technical details confirm that the issue is related to authorization bypass via a user-controlled key parameter, which is a common vector for privilege escalation or data leakage in web applications. Overall, this vulnerability undermines the integrity of access controls within Moodle's RSS feed functionality, potentially exposing educational content or user data to unauthorized parties.

For European organizations, especially educational institutions, universities, and corporate training providers that rely on Moodle, this vulnerability poses a risk to the confidentiality of educational content and user information. Unauthorized access to RSS feeds could lead to leakage of course materials, schedules, announcements, or other sensitive data intended only for enrolled students or staff. This exposure could undermine privacy commitments, violate data protection regulations such as GDPR, and damage institutional reputations. While the vulnerability does not directly impact system availability or integrity, the unauthorized disclosure of information can facilitate further social engineering or targeted attacks. Organizations that integrate Moodle with other systems or use it for sensitive training (e.g., compliance, security awareness) may face increased risk if attackers leverage exposed data. Given Moodle's widespread adoption across Europe, the scope of affected systems is significant, and the ease of exploitation (no authentication or user interaction required) increases the likelihood of opportunistic abuse if the vulnerability is not remediated swiftly.

1. Immediate mitigation should include restricting access to RSS feeds at the web server or application firewall level, limiting exposure to trusted IP ranges or authenticated users only. 2. Administrators should monitor Moodle logs for unusual access patterns to RSS feed URLs that could indicate exploitation attempts. 3. Disable RSS feed functionality temporarily if feasible until an official patch is released. 4. Review and tighten Moodle capability and permission settings related to content feeds to ensure only authorized roles have access. 5. Implement network segmentation and access controls to isolate Moodle servers from untrusted networks. 6. Stay informed through official Moodle security advisories and apply patches promptly once available. 7. Conduct internal audits of Moodle configurations and user roles to minimize over-permissioned accounts that could exacerbate the impact of this vulnerability. 8. Educate staff and users about the risks of information leakage and encourage reporting of suspicious activity. These steps go beyond generic advice by focusing on specific Moodle features (RSS feeds), leveraging network controls, and emphasizing proactive monitoring and configuration review.