What’s Vulnerable › Vulnerabilities

CVE-2021-21241: CSRF can expose users authentication token in Flask-Security-Too

• Severity: high (CVSS 7.4 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.9% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-01-11 · updated 2026-06-17
• Weakness: CWE-352

Description

The Python "Flask-Security-Too" package is used for adding security features to your Flask application. It is an is a independently maintained version of Flask-Security based on the 3.0.0 version of Flask-Security. In Flask-Security-Too from version 3.3.0 and before version 3.4.5, the /login and /change endpoints can return the authenticated user's authentication token in response to a GET request. Since GET requests aren't protected with a CSRF token, this could lead to a malicious 3rd party site acquiring the authentication token. Version 3.4.5 and version 4.0.0 are patched. As a workaround, if you aren't using authentication tokens - you can set the SECURITY_TOKEN_MAX_AGE to "0" (seconds) which should make the token unusable.

Affected products

• Flask-Middleware flask-security-too: from 3.3.0 before 3.4.5 — fixed in 3.4.5

How to fix

Upgrade to a fixed version: Flask-Middleware flask-security-too 3.4.5. Check the vendor advisory for mitigations.

References

• https://github.com/Flask-Middleware/flask-security/commit/61d313150b5f620d0b800896c4f2199005e84b1f
• https://github.com/Flask-Middleware/flask-security/commit/6d50ee9169acf813257c37b75babe9c28e83542a
• https://github.com/Flask-Middleware/flask-security/pull/422
• https://github.com/Flask-Middleware/flask-security/releases/tag/3.4.5
• https://github.com/Flask-Middleware/flask-security/security/advisories/GHSA-hh7m-rx4f-4vpv
• https://pypi.org/project/Flask-Security-Too
• https://github.com/Flask-Middleware/flask-security/commit/61d313150b5f620d0b800896c4f2199005e84b1f
• https://github.com/Flask-Middleware/flask-security/commit/6d50ee9169acf813257c37b75babe9c28e83542a
• https://github.com/Flask-Middleware/flask-security/pull/422
• https://github.com/Flask-Middleware/flask-security/releases/tag/3.4.5
• https://github.com/Flask-Middleware/flask-security/security/advisories/GHSA-hh7m-rx4f-4vpv
• https://pypi.org/project/Flask-Security-Too

Get alerted when CVE-2021-21241 or the next vulnerability affects your stack