CVE-2021-23401Open Redirect
- 5.4MediumCVSS base score
- 1.1%Exploitation in 30 daysEPSS · top 33% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
Description
This affects all versions of package Flask-User. When using the make_safe_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 or \\\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.
Timeline
ID reserved
By snyk
- 6 months later
· 6 months later
Published
- 3 years later
· 3 years later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| snykCNA (assigner) | 3.1 | Medium5.4 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N/E:P/RL:U/RC:C |
| NVDNVD · Modified | 3.1 | Medium6.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N |
- EPSS (exploitation in 30 days)
- 1.1% · top 33% of all CVEs (13 Nov 2026)
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.4.
Affected products
Flask-User
- affected < unspecified
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- PyPIFlask-UserGHSA-4298-89hc-6rfv (opens in a new tab)
References
References3
- https://snyk.io/vuln/SNYK-PYTHON-FLASKUSER-1293188 (opens in a new tab)x_refsource_MISCx_transferred
- https://github.com/lingthio/Flask-User (opens in a new tab)x_refsource_MISCx_transferred
- https://github.com/lingthio/Flask-User/blob/master/flask_user/user_manager__utils.py (opens in a new tab)x_refsource_MISCx_transferred
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2021-0089 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-4298-89hc-6rfv (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2021-23401)Record last updated .