{"cve":"CVE-2021-23393","nvd":{"published":"2021-06-11T00:15:09.273","modified":"2026-06-17T03:38:40.823","status":"Modified","description":"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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N","score":5.4},"cwes":["CWE-601"],"references":["https://github.com/briancappello/flask-unchained/commit/71e36b28166f9ffbe0a991f51127f0984f7e6a40","https://snyk.io/vuln/SNYK-PYTHON-FLASKUNCHAINED-1293189","https://github.com/briancappello/flask-unchained/commit/71e36b28166f9ffbe0a991f51127f0984f7e6a40","https://snyk.io/vuln/SNYK-PYTHON-FLASKUNCHAINED-1293189"],"products":["flask_unchained_project:flask_unchained"],"source":"nvd","synced_at":"2026-10-19T21:20:07.141963181+00:00"},"epss":{"cve":"CVE-2021-23393","score":0.00716,"percentile":0.53794,"date":"2026-11-01"},"kev":null,"osv":[{"id":"GHSA-pjc4-3w99-j7v4","url":"https://osv.dev/vulnerability/GHSA-pjc4-3w99-j7v4","summary":"Open redirect in Flask-Unchained","modified":"2024-09-20T20:25:46.997207Z","packages":[{"ecosystem":"PyPI","name":"flask-unchained","purl":"pkg:pypi/flask-unchained","ranges":["<0.9.0"],"fixed":["0.9.0"]}]},{"id":"PYSEC-2021-96","url":"https://osv.dev/vulnerability/PYSEC-2021-96","summary":"","modified":"2023-11-08T04:05:07.026421Z","packages":[{"ecosystem":"PyPI","name":"flask-unchained","purl":"pkg:pypi/flask-unchained","ranges":["<0.9.0"],"fixed":["0.9.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}