CVE-2021-29621: Flask AppBuilder Observable Response Discrepancy Vulnerability
MODERATECVE-2021-29621 is a MODERATE (CVSS 5.3) observable response discrepancy vulnerability (CWE-203: Observable Discrepancy) affecting Flask AppBuilder libraries in the PyPI ecosystem. The issue involves observable response discrepancy in flask-appbuilder. Remediation is available by upgrading affected packages to version 3.3.0.
CVE-2021-29621 at a Glance
Security Impact
CVSS: 5.3
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N).
How to Fix CVE-2021-29621
To remediate this vulnerability, upgrade all affected Flask AppBuilder dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
pip install Flask-AppBuilder>=3.3.0Run the following command in your project directory to verify that all resolved dependencies use the patched release:
pip show Flask-AppBuilderHow to Check if You Are Affected
To determine whether your Python environment is affected by CVE-2021-29621, inspect your installed packages using pip:
pip show Flask-AppBuilderAnalyze the terminal output to locate any version of Flask AppBuilder in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 3.3.0), your application is affected.
Note: The pip show Flask-AppBuilder command checks currently installed packages in your active Python environment.
Technical Details
Vulnerability Mechanism & Technical Analysis
This vulnerability is classified under CWE-203: Observable Discrepancy, where the product behaves differently or sends different responses under different circumstances in a way that is observable to an unauthorized actor. In Flask AppBuilder, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.
Source Advisory Statement
CVE-2021-29621 Affected Flask AppBuilder Versions
1 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
Flask-AppBuilder
|
PyPI |
< 3.3.0
|
3.3.0
|
References
Frequently Asked Questions
What is CVE-2021-29621?
Which Flask AppBuilder versions are affected?
What version fixes CVE-2021-29621?
Is Flask-AppBuilder affected?
What is the CVSS score of CVE-2021-29621?
What CWE is associated with CVE-2021-29621?
How can I check PyPI dependencies for CVE-2021-29621?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-434h-p4gx-jm89",
"modified" : "2025-03-07T19:08:59Z",
"published" : "2021-05-27T18:38:36Z",
"aliases" : [ "CVE-2021-29621" ],
"summary" : "Observable Response Discrepancy in Flask-AppBuilder",
"details" : "### Impact\nUser 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.\n\n### Patches\nUpgrade to 3.3.0\n\n### For more information\nIf you have any questions or comments about this advisory:\n* Open an issue in [Flask-AppBuilder](https://github.com/dpgaspar/Flask-AppBuilder)",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N"
}, {
"type" : "CVSS_V4",
"score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "PyPI",
"name" : "Flask-AppBuilder"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"fixed" : "3.3.0"
} ]
} ]
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/dpgaspar/Flask-AppBuilder/security/advisories/GHSA-434h-p4gx-jm89"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-29621"
}, {
"type" : "WEB",
"url" : "https://github.com/dpgaspar/Flask-AppBuilder/commit/780bd0e8fbf2d36ada52edb769477e0a4edae580"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/dpgaspar/Flask-AppBuilder"
}, {
"type" : "WEB",
"url" : "https://github.com/pypa/advisory-database/tree/main/vulns/flask-appbuilder/PYSEC-2021-90.yaml"
}, {
"type" : "WEB",
"url" : "https://lists.apache.org/thread.html/r466759f377651f0a690475d5a52564d0e786e82c08d5a5730a4f8352%40%3Cannounce.apache.org%3E"
}, {
"type" : "WEB",
"url" : "https://lists.apache.org/thread.html/r466759f377651f0a690475d5a52564d0e786e82c08d5a5730a4f8352@%3Cannounce.apache.org%3E"
}, {
"type" : "WEB",
"url" : "https://lists.apache.org/thread.html/r5b754118ba4e996adf03863705d34168bffec202da5c6bdc9bf3add5%40%3Cannounce.apache.org%3E"
}, {
"type" : "WEB",
"url" : "https://lists.apache.org/thread.html/r5b754118ba4e996adf03863705d34168bffec202da5c6bdc9bf3add5@%3Cannounce.apache.org%3E"
}, {
"type" : "WEB",
"url" : "https://lists.apache.org/thread.html/r91067f953906d93aaa1c69fe2b5472754019cc6bd4f1ba81349d62a0%40%3Ccommits.airflow.apache.org%3E"
}, {
"type" : "WEB",
"url" : "https://lists.apache.org/thread.html/r91067f953906d93aaa1c69fe2b5472754019cc6bd4f1ba81349d62a0@%3Ccommits.airflow.apache.org%3E"
}, {
"type" : "WEB",
"url" : "https://pypi.org/project/Flask-AppBuilder"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-203" ],
"severity" : "MODERATE",
"github_reviewed" : true,
"github_reviewed_at" : "2021-05-25T20:21:31Z",
"nvd_published_at" : "2021-06-07T19:15:00Z"
}
}