CVE-2022-24880: Potential Captcha Validate Bypass in flask-session-captcha

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2022-04-25 · updated 2026-06-17
Weakness: CWE-253

Description

flask-session-captcha is a package which allows users to extend Flask by adding an image based captcha stored in a server side session. In versions prior to 1.2.1, he `captcha.validate()` function would return `None` if passed no value (e.g. by submitting an having an empty form). If implementing users were checking the return value to be **False**, the captcha verification check could be bypassed. Version 1.2.1 fixes the issue. Users can workaround the issue by not explicitly checking that the value is False. Checking the return value less explicitly should still work.

Affected products

Tethik flask-session-captcha: before 1.2.1 — fixed in 1.2.1

How to fix

Upgrade to a fixed version: Tethik flask-session-captcha 1.2.1. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2022-24880 or the next vulnerability affects your stack