CVE-2023-40021 Information

Description

Oppia is an online learning platform. When comparing a received CSRF token against the expected token Oppia uses the string equality operator (==) which is not safe against timing attacks. By repeatedly submitting invalid tokens an attacker can brute-force the expected CSRF token character by character. Once they have recovered the token they can then submit a forged request on behalf of a logged-in user and execute privileged actions on that user’s behalf. In particular the function to validate received CSRF tokens is at oppia.core.controllers.base.CsrfTokenManager.is_csrf_token_valid. An attacker who can lure a logged-in Oppia user to a malicious website can perform any change on Oppia that the user is authorized to do including changing profile information; creating deleting and changing explorations; etc. Note that the attacker cannot change a user’s login credentials. An attack would need to complete within 1 second because every second the time used in computing the token changes. This issue has been addressed in commit b89bf80837 which has been included in release 3.3.2-hotfix-2. Users are advised to upgrade. There are no known workarounds for this vulnerability.

Reference

https://github.com/oppia/oppia/blob/3a05c3558a292f3db9e658e60e708c266c003fd0/core/controllers/base.py#L964-L990 https://github.com/oppia/oppia/commit/b89bf808378c1236874b5797a7bda32c77b4af23 https://github.com/oppia/oppia/pull/18769 https://github.com/oppia/oppia/security/advisories/GHSA-49jp-pjc3-2532