Open redirect in Flask-Unchained
Priority LOW 26CWE-601Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- Required
- Attack complexity
- Low
- Impact type
- Spoofing
- Confidentiality · integrity · availability
- Low · Low · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-601.
Summary
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.
Why it matters now
EPSS 0.00716 54th percentileScored 2026-11-07
Fix Fixed Flask-Unchained: 0.9.0Flask-Unchained (PyPI): 0.9.0
SSVC decision points
Not available: CISA has not published SSVC decision points for this record.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| — | Flask-Unchained | before 0.9.0 | 0.9.0 | Patch available | CNA |
| — | Flask-Unchained (PyPI) | before 0.9.0 | 0.9.0 | Patch available | GHSA-pjc4-3w99-j7v4 |
- Flask-Unchained Vendor— Affected before 0.9.0 Fixed in 0.9.0 Patch available CNA
- Flask-Unchained (PyPI) Vendor— Affected before 0.9.0 Fixed in 0.9.0 Patch available GHSA-pjc4-3w99-j7v4
CPE configurations NVD · 1
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:flask_unchained_project:flask_unchained:*:*:*:*:*:*:*:* | before 0.9.0 | Vulnerable | Flask Unchained Project |
- cpe:2.3:a:flask_unchained_project:flask_unchained:*:*:*:*:*:*:*:* Versions before 0.9.0 Vulnerable ·Flask Unchained Project
Remediation
- Fix · CNA Flask-Unchained Fixed in 0.9.0
- Fix · GHSA-pjc4-3w99-j7v4 Flask-Unchained (PyPI) Fixed in 0.9.0 Advisory →
Timeline
- 2026-10-02 Threatist record created from CVE-2021-23393
- 2026-10-03 Alias added: GHSA-pjc4-3w99-j7v4
References
Patch 1
Advisory 2
Sources
- CVE-2021-23393 · CVE Program
- CVE-2021-23393 · NVD
- FIRST EPSS
- GHSA-pjc4-3w99-j7v4 · GitHub Advisory Database · CC BY 4.0
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