Details

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.

Severity

Unknown

References

• https://github.com/pallets/flask/commit/70f906c51ce49c485f1d355703e9cc3386b1cc2b
• https://github.com/pallets/flask/releases/tag/2.3.2
• https://github.com/pallets/flask/releases/tag/2.2.5
• https://github.com/pallets/flask/security/advisories/GHSA-m2qf-hxjv-5gpq
• https://github.com/pallets/flask/commit/afd63b16170b7c047f5758eb910c416511e9c965

This data is provided by OSV and the PyPI Advisory Database (CC-BY 4.0).

Details

When all of the following conditions are met, a response containing data intended for one client may be cached and subsequently sent by a 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 is 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.

Severity

• CVSS Score: 7.5 / 10 (High)
• Vector String: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

References

• https://github.com/pallets/flask/security/advisories/GHSA-m2qf-hxjv-5gpq
• https://nvd.nist.gov/vuln/detail/CVE-2023-30861
• https://github.com/pallets/flask/commit/70f906c51ce49c485f1d355703e9cc3386b1cc2b
• https://github.com/pallets/flask/commit/afd63b16170b7c047f5758eb910c416511e9c965
• https://github.com/pallets/flask
• https://github.com/pallets/flask/releases/tag/2.2.5
• https://github.com/pallets/flask/releases/tag/2.3.2
• https://github.com/pypa/advisory-database/tree/main/vulns/flask/PYSEC-2023-62.yaml
• https://lists.debian.org/debian-lts-announce/2023/08/msg00024.html
• https://security.netapp.com/advisory/ntap-20230818-0006
• https://www.debian.org/security/2023/dsa-5442

This data is provided by OSV and the GitHub Advisory Database (CC-BY 4.0).

v2.2.5

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Released 2023-05-02

• Update for compatibility with Werkzeug 2.3.3.
• Set Vary: Cookie header when the session is accessed, modified, or refreshed.

v2.2.4

Compare Source

Released 2023-04-25

• Update for compatibility with Werkzeug 2.3.

v2.2.3

Compare Source

Released 2023-02-15

• Autoescape is enabled by default for .svg template files. :issue:4831
• Fix the type of template_folder to accept pathlib.Path. :issue:4892
• Add --debug option to the flask run command. :issue:4777

v2.2.2

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Released 2022-08-08

• Update Werkzeug dependency to >= 2.2.2. This includes fixes related
  to the new faster router, header parsing, and the development
  server. :pr:4754
• Fix the default value for app.env to be "production". This
  attribute remains deprecated. :issue:4740

v2.2.1

Compare Source

Released 2022-08-03

• Setting or accessing json_encoder or json_decoder raises a
  deprecation warning. :issue:4732