PT-2026-21353 · Flask+2 · Flask+2
CVSS v3.1
9.8
Critical
| Vector | AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
Name of the Vulnerable Software and Affected Versions
Flask versions 3.1.2 and below
Description
Flask, a web server gateway interface (WSGI) web application framework, may improperly handle caching when accessing the session object. Specifically, it may fail to set the 'Vary: Cookie' header, potentially leading to a Use of Cache Containing Sensitive Information issue. This occurs when the application is hosted behind a caching proxy that doesn't ignore responses with cookies, lacks a 'Cache-Control' header to mark pages as private or non-cacheable, and accesses the session in a way that only touches keys without reading values or mutating the session. The issue stems from overlooking certain forms of access, such as the Python 'in' operator.
Recommendations
Update to Flask version 3.1.3 or later.
Exploit
Fix
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Weakness Enumeration
Related Identifiers
Affected Products
Flask
Linuxmint
Ubuntu