CVE-2023-40021

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in, but needs a user to act. High risk of data tampering.

Exploit odds

0.8% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2023-08-16 21:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-11-10 12:10 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.8% in the next 30 days (EPSS).
• Severity: 5.3 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2023-08-16 21:15 UTC

Last modified

2026-11-10 12:10 UTC

Exploit probability

0.8% · EPSS, next 30 days

Weakness

CWE-203

Record status

Modified

Affected

• Oppia < 3.3.2
• Oppia 3.3.2

Attack profile CVSS 3.1 · 5.3

Attack vector

Network

Complexity

High

Privileges needed

None

User interaction

Required

Scope

Unchanged

Confidentiality

None

Integrity

High

Availability

None

Is it in your code?

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Read https://cve-list.com/agent/cve/CVE-2023-40021.md and follow it. Check whether this project is affected by CVE-2023-40021. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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