---
id: CVE-2021-41265
aliases:
  - GHSA-m3rf-7m4w-r66q
  - PYSEC-2021-851
title: Improper Authentication in Flask-AppBuilder
summary: Improper Authentication in Flask-AppBuilder
severity: high
cvss: 8.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N'
vendor: flask-appbuilder
product: flask-appbuilder
ecosystem: pip
affected:
  - flask-appbuilder < 3.3.4
patched:
  - flask-appbuilder 3.3.4
published: '2021-12-09'
updated: '2026-07-08'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-m3rf-7m4w-r66q'
references:
  - url: >-
      https://github.com/dpgaspar/Flask-AppBuilder/security/advisories/GHSA-m3rf-7m4w-r66q
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2021-41265'
  - url: >-
      https://github.com/dpgaspar/Flask-AppBuilder/commit/eba517aab121afa3f3f2edb011ec6bc4efd61fbc
  - url: 'https://github.com/dpgaspar/Flask-AppBuilder'
  - url: 'https://github.com/dpgaspar/Flask-AppBuilder/releases/tag/v3.3.4'
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/flask-appbuilder/PYSEC-2021-851.yaml
tags:
  - osv
  - pip
epss: 0.01285
epssPercentile: 0.6889
ingestedAt: '2026-07-08T18:25:51.102Z'
---

## Overview

### Impact
Improper authentication on the REST API. Allows for a malicious actor with a carefully crafted request to successfully authenticate and gain access to existing protected REST API endpoints. Only affects non database authentication types, and new REST API endpoints.

### Patches
Upgrade to Flask-AppBuilder 3.3.4

### For more information
If you have any questions or comments about this advisory:
* Open an issue in https://github.com/dpgaspar/Flask-AppBuilder

## Affected packages

- `flask-appbuilder < 3.3.4`

## Remediation

Upgrade to a patched release:

- `flask-appbuilder 3.3.4`