Wrkzeug's incorrect parsing of nameless cookies leads to __Host- cookies bypass
Priority LOW 17CWE-20Published · Updated
Key facts
- Attack vector
- Adjacent network
- Privileges required
- None
- User interaction
- Required
- Attack complexity
- Low
- Impact type
- —
- Confidentiality · integrity · availability
- None · Low · None
- Fix status
- Partial Red Hat: 3 fixed, 8 without a fix
Attack profile from CVSS 3.1 · NVD. Fix status from CNA, GitHub and Red Hat.
Summary
Werkzeug is a comprehensive WSGI web application library. 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 prior to 2.2.3 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. The issue is fixed in Werkzeug 2.2.3.
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00507 43rd percentileScored 2026-11-07
Fix Partial werkzeug (pallets): 2.2.3Werkzeug (PyPI): 2.2.3Red Hat: 3 advisoriesRed Hat: 3 fixed, 8 without a fix
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| pallets | werkzeug | before 2.2.3 | 2.2.3 | Patch available | CNA |
| — | Werkzeug (PyPI) | before 2.2.3 | 2.2.3 | Patch available | GHSA-px8h-6qxv-m22q |
- werkzeug Vendorpallets Affected before 2.2.3 Fixed in 2.2.3 Patch available CNA
- Werkzeug (PyPI) Vendor— Affected before 2.2.3 Fixed in 2.2.3 Patch available GHSA-px8h-6qxv-m22q
Remediation
- Fix · CNA werkzeug (pallets) Fixed in 2.2.3
- Fix · GHSA-px8h-6qxv-m22q Werkzeug (PyPI) Fixed in 2.2.3 Advisory →
Red Hat 3 advisories
- RHSA-2025:9775 Released 2025-06-26 · Red Hat rating ImportantRed Hat Ceph Storage 8.1 security, bug fix, and enhancement updates
- Red Hat Ceph Storage 8.1 Tools ceph-2:19.2.1-222.el9cp, ceph-base-2:19.2.1-222.el9cp, ceph-common-2:19.2.1-222.el9cp +28
- RHSA-2025:4664 Released 2025-05-07 · Red Hat rating ImportantRed Hat Ceph Storage 7.1 security, bug fix, and enhancement updates
- Red Hat Ceph Storage 7.1 Tools ceph-2:18.2.1-329.el8cp, ceph-2:18.2.1-329.el9cp, ceph-base-2:18.2.1-329.el8cp +47
- RHSA-2023:1018 Released 2023-02-28 · Red Hat rating ImportantRed Hat OpenStack Platform 17.0 (python-werkzeug) security update
- Red Hat OpenStack Platform 17.0 python-werkzeug-2.0.1-5.el9ost, python3-werkzeug-2.0.1-5.el9ost
Vendor assessments
Red Hat
Red Hat rating: Low. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 7 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 8 | Affected | No fix yet: Fix deferred |
| Red Hat OpenShift Container Platform 4 | Affected | No fix yet |
| Red Hat OpenStack Platform 16.1 | Affected | No fix yet: Fix deferred |
| Red Hat OpenStack Platform 16.2 | Affected | No fix yet: Fix deferred |
| Red Hat Quay 3 | Affected | No fix yet: Fix deferred |
| Red Hat Storage 3 | Affected | No fix planned: Out of support scope |
| Red Hat Update Infrastructure 3 for Cloud Providers | Affected | No fix planned: Out of support scope |
| Red Hat Ceph Storage 7.1 Tools | Fixed | RHSA-2025:4664 |
| Red Hat Ceph Storage 8.1 Tools | Fixed | RHSA-2025:9775 |
| Red Hat OpenStack Platform 17.0 | Fixed | RHSA-2023:1018 |
Not affected: 2 products
- Red Hat Ceph Storage 7.1 Tools
- Red Hat Ceph Storage 8.1 Tools
Timeline
- 2026-10-02 Threatist record created from CVE-2023-23934
- 2026-10-03 Alias added: GHSA-px8h-6qxv-m22q
References
Advisory 2
Other 6
- https://github.com/pallets/werkzeug/releases/tag/2.2.3
- https://www.debian.org/security/2023/dsa-5470
- https://security.netapp.com/advisory/ntap-20230818-0003/
- 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
More pallets Werkzeug vulnerabilities
- TI-2019-10671 In Pallets Werkzeug before 0.15.5, SharedDataMiddleware mishandles drive names (such as C:) in Windows pathnames. CVSS 3.1HIGH 7.5
- TI-2022-11856 Improper parsing of HTTP requests in Pallets Werkzeug v2.1.0 and below allows attackers… CVSS 3.1CRITICAL 9.8
- TI-2023-10880 Werkzeug may allow high resource usage when parsing multipart form data with many fields CVSS 3.1HIGH 7.5
- TI-2024-22527 Werkzeug's improper usage of a pathname and improper CSRF protection results in the remote command execution CVSS 3.1HIGH 7.5
- TI-2024-33234 Werkzeug possible resource exhaustion when parsing file data in forms CVSS 4.0MEDIUM 6.9
- TI-2023-24778 Uncontrolled resource consumption in pallets werkzeug CVSS 3.1HIGH 8.0
Sources
- CVE-2023-23934 · CVE Program
- CVE-2023-23934 · NVD
- FIRST EPSS
- GHSA-px8h-6qxv-m22q · GitHub Advisory Database · CC BY 4.0
- CVE-2023-23934 · Red Hat security data · CC BY 4.0
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