Incorrect parsing of nameless cookies leads to __Host- cookies bypass
Browsers may allow "nameless" cookies that look like =value instead of key=value. A vulnerable browser may allow a compromised application on an adjacent subdomain to exploit this to set a cookie like =__Host-test=bad for another subdomain.
Werkzeug <= 2.2.2 will parse the cookie =__Host-test=bad as __Host-test=bad. If a Werkzeug application is running next to a vulnerable or malicious subdomain which sets such a cookie using a vulnerable browser, the Werkzeug application will see the bad cookie value but the valid cookie key.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | werkzeug | < 2.2.3 | 2.2.3 |
References
- https://github.com/pallets/werkzeug/security/advisories/GHSA-px8h-6qxv-m22q
- https://github.com/pallets/werkzeug/commit/cf275f42acad1b5950c50ffe8ef58fe62cdce028
- https://github.com/pallets/werkzeug/releases/tag/2.2.3
- https://nvd.nist.gov/vuln/detail/CVE-2023-23934
- https://github.com/pallets/werkzeug
- https://github.com/pypa/advisory-database/tree/main/vulns/werkzeug/PYSEC-2023-57.yaml
- https://security.netapp.com/advisory/ntap-20230818-0003
- https://www.debian.org/security/2023/dsa-5470
- CVSS vector
CVSS:3.1/AV:A/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:N- Weakness (CWE)
CWE-20- Platform
- Python (PyPI)
- Package
werkzeug- Disclosed
- 14.02.2023
- Updated
- 11.10.2026 15:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2023-57 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-px8h-6qxv-m22q - CC BY 4.0
Vulnerability history: werkzeug
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 15
- First → latest
- 10.2017 10.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 4
- Medium 9
- Low 1
- Unrated 1
Disclosures per year
- 2017: 1
- 2018: 0
- 2019: 1
- 2020: 1
- 2021: 0
- 2022: 2
- 2023: 3
- 2024: 3
- 2025: 1
- 2026: 3
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Incorrect parsing of nameless cookies leads to __Host- cookies bypass this entry
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