Open redirect in Flask-Unchained
This affects the package Flask-Unchained before 0.9.0. When using the the _validate_redirect_url function, it is possible to bypass URL validation and redirect a user to an arbitrary URL by providing multiple back slashes such as \\evil.com/path. This vulnerability is only exploitable if an alternative WSGI server other than Werkzeug is used, or the default behaviour of Werkzeug is modified using 'autocorrect_location_header=False.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | flask-unchained | < 0.9.0 | 0.9.0 |
References
- https://snyk.io/vuln/SNYK-PYTHON-FLASKUNCHAINED-1293189
- https://github.com/briancappello/flask-unchained/commit/71e36b28166f9ffbe0a991f51127f0984f7e6a40
- https://github.com/advisories/GHSA-pjc4-3w99-j7v4
- https://nvd.nist.gov/vuln/detail/CVE-2021-23393
- https://github.com/briancappello/flask-unchained/commit/2bfeedf1bc31df851cab8c66df0c432b10406aad
- https://github.com/pypa/advisory-database/tree/main/vulns/flask-unchained/PYSEC-2021-96.yaml
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N- Weakness (CWE)
CWE-601- Platform
- Python (PyPI)
- Package
flask-unchained- Disclosed
- 11.06.2021
- Updated
- 11.10.2026 11:20
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2021-96 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-pjc4-3w99-j7v4 - CC BY 4.0
Vulnerability history: flask-unchained
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
This is the only known vulnerability of this package.
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