CVE-2023-23934: Werkzeug is a comprehensive WSGI web application library. Browsers may allow "nameless" cookies that look like `=value` instead of `key=value`. A vuln...

Description

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.

Metrics

CVSS 3.1

3.5/10

CVSS:3.1/AV:A/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

EPSS Probability

0.51%

39.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-20

Affected Software

Vendor	Product	Versions
Palletsprojects	Werkzeug	< 2.2.3

References

Timeline

Published: Feb 14, 2023
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2023-23934?

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.

How severe is CVE-2023-23934?

CVE-2023-23934 has a CVSS score of 3.5/10 (LOW severity). The EPSS model estimates a 0.51% probability of exploitation in the next 30 days.

How do I fix CVE-2023-23934?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.