CVE-2021-23393 json
Open Redirect
published 2021-06-10 5 y ago modified 2026-06-17 4 mo ago also GHSA-pjc4-3w99-j7v4 , PYSEC-2021-96 , EUVD-2021-0088
- cvss
- 5.4
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.7%
- EPSS 0.7% chance of exploitation in 30 days, percentile 54%
- public exploits
- 0
- none known
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.
Patch / fix
- pypi flask-unchained 0.9.0
- n/a Flask-Unchained 0.9.0
Exploit prediction
0.72% chance of exploitation in the next 30 days, higher than 54% of all scored CVEs (FIRST EPSS, 2026-11-08).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 5.4 | 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 |
| CNA | 3.1 | 5.4 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N |
| NVD | 3.1 | 5.4 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N |
| NVD | 2.0 | 5.8 | AV:N/AC:M/Au:N/C:P/I:P/A:N |
| GitHub | 3.1 | 5.4 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| pypi | flask-unchained | <0.9.0 |
0.9.0 |
Affected products
- n/a Flask-Unchained
Classification
- Weakness
-
- CWE-601 URL Redirection to Untrusted Site
References
-
github.com
/briancappello/flask-unchained/commit/71e36b28166f9ffbe0a991f51127f0984f7e6a40
web, patch, third-party-advisory
-
snyk.io
/vuln/SNYK-PYTHON-FLASKUNCHAINED-1293189
web, patch, third-party-advisory, advisory
-
github.com
/briancappello/flask-unchained/commit/2bfeedf1bc31df851cab8c66df0c432b10406aad
web
-
nvd.nist.gov
/vuln/detail/CVE-2021-23393
advisory
-
github.com
/advisories/GHSA-pjc4-3w99-j7v4
advisory
-
github.com
/pypa/advisory-database/tree/main/vulns/flask-unchained/PYSEC-2021-96.yaml
web
Sources
- CVE List CVE-2021-23393
- GitHub Advisory GHSA-pjc4-3w99-j7v4
- NVD CVE-2021-23393
- OSV PYSEC-2021-96
Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.