CVE-2023-40021
When comparing a received CSRF token against the expected token, Oppia uses the string equality operator (`==`), which is not safe against timing attacks.
Does this matter?
Lower severity and a low EPSS score (0.77%). Track it; it rarely justifies an emergency change on its own.
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.
- CVSS 3.1
- 5.3 MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N
- EPSS
- 0.77% probability · 54th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-203, CWE-208
- Affected
- oppia/oppia
- Source
- security-advisories@github.com
References
- https://github.com/oppia/oppia/blob/3a05c3558a292f3db9e658e60e708c266c003fd0/core/controllers/base.py#L964-L990Product
- https://github.com/oppia/oppia/commit/b89bf808378c1236874b5797a7bda32c77b4af23Patch
- https://github.com/oppia/oppia/pull/18769Patch
- https://github.com/oppia/oppia/security/advisories/GHSA-49jp-pjc3-2532Exploit, Vendor Advisory
- https://github.com/oppia/oppia/blob/3a05c3558a292f3db9e658e60e708c266c003fd0/core/controllers/base.py#L964-L990Product
- https://github.com/oppia/oppia/commit/b89bf808378c1236874b5797a7bda32c77b4af23Patch
- https://github.com/oppia/oppia/pull/18769Patch
- https://github.com/oppia/oppia/security/advisories/GHSA-49jp-pjc3-2532Exploit, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.