CVE-2026-27205: Use of Cache Containing Sensitive Information

Flask is a web server gateway interface WSGI web application framework. In versions 3.1.2 and below, when the session object is accessed, Flask should set the Vary: Cookie header., resulting in a Use of Cache Containing Sensitive Information vulnerability. The logic instructs caches not to cache...

Flask session does not add `Vary: Cookie` header when accessed in some ways

When the session object is accessed, Flask should set the Vary: Cookie header. This instructs caches not to cache the response, as it may contain information specific to a logged in user. This is handled in most cases, but some forms of access such as the Python in operator were overlooked. The...