CVE-2023-30861

Flask is a lightweight WSGI web application framework. When all of the
following conditions are met, a response containing data intended for one
client may be cached and subsequently sent by the proxy to other clients.
If the proxy also caches Set-Cookie headers, it may send one client’s
session cookie to other clients. The severity depends on the
application’s use of the session and the proxy’s behavior regarding
cookies. The risk depends on all these conditions being met. 1. The
application must be hosted behind a caching proxy that does not strip
cookies or ignore responses with cookies. 2. The application sets
session.permanent = True 3. The application does not access or modify the
session at any point during a request. 4. SESSION_REFRESH_EACH_REQUEST
enabled (the default). 5. The application does not set a Cache-Control
header to indicate that a page is private or should not be cached. This
happens because vulnerable versions of Flask only set the Vary: Cookie
header when the session is accessed or modified, not when it is refreshed
(re-sent to update the expiration) without being accessed or modified. This
issue has been fixed in versions 2.3.2 and 2.2.5.

Bugs

• <http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1035670&gt;