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.
Published 2023-08-16 21:15:10
Updated 2023-08-25 20:08:18
Source GitHub, Inc.
View at NVD,   CVE.org
Vulnerability category: Cross-site request forgery (CSRF)

Exploit prediction scoring system (EPSS) score for CVE-2023-40021

0.05%
Probability of exploitation activity in the next 30 days EPSS Score History
~ 20 %
Percentile, the proportion of vulnerabilities that are scored at or less

CVSS scores for CVE-2023-40021

Base Score Base Severity CVSS Vector Exploitability Score Impact Score Score Source First Seen
5.3
MEDIUM CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N
1.6
3.6
NIST
5.3
MEDIUM CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N
1.6
3.6
GitHub, Inc.

CWE ids for CVE-2023-40021

  • The product behaves differently or sends different responses under different circumstances in a way that is observable to an unauthorized actor, which exposes security-relevant information about the state of the product, such as whether a particular operation was successful or not.
    Assigned by:
    • nvd@nist.gov (Primary)
    • security-advisories@github.com (Secondary)
  • Two separate operations in a product require different amounts of time to complete, in a way that is observable to an actor and reveals security-relevant information about the state of the product, such as whether a particular operation was successful or not.
    Assigned by: security-advisories@github.com (Secondary)

References for CVE-2023-40021

Products affected by CVE-2023-40021

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