SessFix in Moodle 3.x-3.11.18 via unauth sesskey in OAuth2
CVE-2025-53021 Published on June 24, 2025
A session fixation vulnerability in Moodle 3.x through 3.11.18 allows unauthenticated attackers to hijack user sessions via the sesskey parameter. The sesskey can be obtained without authentication and reused within the OAuth2 login flow, resulting in the victim's session being linked to the attacker's. Successful exploitation results in full account takeover. According to the Moodle Releases page, "Bug fixes for security issues in 3.11.x ended 11 December 2023." NOTE: This vulnerability only affects products that are no longer supported by the maintainer.
Weakness Type
Session Fixation
Authenticating a user, or otherwise establishing a new user session, without invalidating any existing session identifier gives an attacker the opportunity to steal authenticated sessions.
Products Associated with CVE-2025-53021
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Affected Versions
Moodle:- Version 3, <= 3.11.18 is affected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.