CVE-2023-40021

Date: August 16, 2023

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.

Language: Python