# CVE-2021-29621: Observable Response Discrepancy in Flask-AppBuilder

Source: https://junglewise.ai/threats/cve-2021-29621-observable-response-discrepancy-in-flask-appbuilder  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2021-06-07  
License: CC BY 4.0 with a link back

CVE-2021-29621 · Severity: low · CVSS 3.1 · Published 2021-06-07

Flask-AppBuilder is a development framework, built on top of Flask. User enumeration in database authentication in Flask-AppBuilder <= 3.2.3. Allows for a non authenticated user to enumerate existing accounts by timing the response time from the server when you are logging in. Upgrade to version 3.3.0 or higher to resolve.

Technologies: [flask-appbuilder (PyPI)](https://junglewise.ai/threats/technologies/flask-appbuilder). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2021-29621 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2021-29621 being exploited in the wild.

**How severe is CVE-2021-29621?** Low severity, with a CVSS score of 3.1, published 7 June 2021.

**Which products and versions are affected?** flask-appbuilder (PyPI) ECOSYSTEM:introduced=0,fixed=3.3.0, GIT:introduced=0,fixed=780bd0e8fbf2d36ada52edb769477e0a4edae580|ECOSYSTEM:introduced=0,fixed=3.3.0.

**Is there a fix for CVE-2021-29621?** Yes. flask-appbuilder (PyPI): upgrade to 3.3.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2021-29621?** Check whether you run flask-appbuilder (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- flask-appbuilder (PyPI): upgrade to 3.3.0 or later

  ```sh
  pip install "flask-appbuilder>=3.3.0"
  ```


## Affected products

- flask-appbuilder (PyPI) ECOSYSTEM:introduced=0,fixed=3.3.0, GIT:introduced=0,fixed=780bd0e8fbf2d36ada52edb769477e0a4edae580|ECOSYSTEM:introduced=0,fixed=3.3.0

## Identifiers

- CVE-2021-29621
- GHSA-434h-p4gx-jm89
- PYSEC-2021-90

## Related threats

- [PYSEC-2026-1378 - Flask App Builder has an Authentication Bypass vulnerability when using non AUTH_DB methods](https://junglewise.ai/threats/cve-2025-58065-flask-app-builder-has-an-authentication-bypass-vulnerability-when)
- [PYSEC-2026-1379 - Flask-AppBuilder open redirect vulnerability using HTTP host injection](https://junglewise.ai/threats/cve-2025-32962-flask-appbuilder-open-redirect-vulnerability-using-http-host)
- [PYSEC-2026-1382 - Flask-AppBuilder's login form allows browser to cache sensitive fields](https://junglewise.ai/threats/cve-2024-45314-flask-appbuilder-s-login-form-allows-browser-to-cache-sensitive)
- [PYSEC-2026-1381 - Flask-AppBuilder's OAuth login page subject to Cross Site Scripting (XSS)](https://junglewise.ai/threats/cve-2024-27083-flask-appbuilder-s-oauth-login-page-subject-to-cross-site)
- [PYSEC-2026-1380 - Flask-AppBuilder Has No Rate Limiting on Login AUTH DB](https://junglewise.ai/threats/cve-2023-29005-flask-appbuilder-has-no-rate-limiting-on-login-auth-db)