Information Exposure Through Persistent Cookies Affecting flask package, versions <2.2.2-3


Severity

Recommended
0.0
high
0
10

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Threat Intelligence

EPSS
0.23% (62nd percentile)

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  • Snyk IDSNYK-DEBIANUNSTABLE-FLASK-5490766
  • published3 May 2023
  • disclosed2 May 2023

Introduced: 2 May 2023

CVE-2023-30861  (opens in a new tab)
CWE-539  (opens in a new tab)

How to fix?

Upgrade Debian:unstable flask to version 2.2.2-3 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream flask package and not the flask package as distributed by Debian. See How to fix? for Debian:unstable relevant fixed versions and status.

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.

CVSS Scores

version 3.1