title: Wrkzeug's incorrect parsing of nameless cookies leads to __Host- cookies bypass
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.
problem types: CWE-20: Improper Input Validation
affected:
{
vendor: pallets
product: werkzeug
versions:
version: < 2.2.3, status: affected
}
metrics:
cvssV3_1: [
attackComplexity: HIGH
attackVector: ADJACENT_NETWORK
availabilityImpact: NONE
baseScore: 2.6
baseSeverity: LOW
confidentialityImpact: NONE
integrityImpact: LOW
privilegesRequired: NONE
scope: UNCHANGED
userInteraction: REQUIRED
vectorString: CVSS:3.1/AV:A/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:N
version: 3.1
]