Timing Attack Reveals CSRF Tokens in oppia

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/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N

通过差异性导致的信息暴露

Oppia 安全漏洞

Oppia是一种在线学习工具。用于轻松创建和共享交互式活动。 Oppia 1.1.0 到 3.3.2版本存在安全漏洞，该漏洞源于当将收到的 CSRF 令牌与预期令牌进行比较时，使用字符串相等运算符 ==，攻击者利用该漏洞可以通过重复提交无效令牌，逐个字符地暴力破解预期的 CSRF 令牌。

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