Update dependency flask to v3.1.3 [SECURITY]

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
flask (changelog)	==3.1.1 → ==3.1.3

GitHub Vulnerability Alerts

CVE-2026-27205

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 severity depends on the application's use of the session, and the cache'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 ignore responses with cookies.
2. The application does not set a Cache-Control header to indicate that a page is private or should not be cached.
3. The application accesses the session in a way that does not access the values, only the keys, and does not mutate the session.

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Release Notes

pallets/flask (flask)

v3.1.3

Compare Source

Released 2026-02-18

• The session is marked as accessed for operations that only access the keys
  but not the values, such as in and len. :ghsa:68rp-wp8r-4726

v3.1.2

Compare Source

Released 2025-08-19

• stream_with_context does not fail inside async views. :issue:5774
• When using follow_redirects in the test client, the final state
  of session is correct. :issue:5786
• Relax type hint for passing bytes IO to send_file. :issue:5776

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