high
7.5
CWE
539
Advisory Published
CVE Published
Updated

CVE-2023-30861: Flask vulnerable to possible disclosure of permanent session cookie due to missing Vary: Cookie header

First published: Mon May 01 2023(Updated: )

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.

Credit: security-advisories@github.com security-advisories@github.com security-advisories@github.com

Affected SoftwareAffected VersionHow to fix
Palletsprojects Flask<2.2.5
Palletsprojects Flask>=2.3.0<2.3.2
debian/flask<=1.0.2-3
1.0.2-3+deb10u1
1.1.2-2+deb11u1
2.2.2-3
2.2.5-1
pip/flask<2.2.5
2.2.5
pip/flask>=2.3.0<2.3.2
2.3.2
redhat/flask<2.2.5
2.2.5
redhat/flask<2.3.2
2.3.2
IBM Watson Knowledge Catalog on-prem<=4.x
<2.2.5
>=2.3.0<2.3.2

Remedy

https://github.com/pallets/flask/commit/70f906c51ce49c485f1d355703e9cc3386b1cc2b

Remedy

https://github.com/pallets/flask/commit/afd63b16170b7c047f5758eb910c416511e9c965

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Reference Links

Parent vulnerabilities

(Appears in the following advisories)

Frequently Asked Questions

  • What is CVE-2023-30861?

    CVE-2023-30861 is a vulnerability in Pallets Flask that could allow a remote attacker to obtain sensitive information.

  • What is the severity of CVE-2023-30861?

    The severity of CVE-2023-30861 is high with a CVSS score of 7.5.

  • How does CVE-2023-30861 affect Pallets Flask?

    CVE-2023-30861 affects Pallets Flask versions 2.2.5 up to, but excluding, 2.3.2.

  • How can I fix CVE-2023-30861?

    To fix CVE-2023-30861, update Pallets Flask to version 2.3.2 or apply a suitable remedy provided by your distribution.

  • Where can I find more information about CVE-2023-30861?

    You can find more information about CVE-2023-30861 in the following references: - [GitHub Commit](https://github.com/pallets/flask/commit/70f906c51ce49c485f1d355703e9cc3386b1cc2b) - [Flask 2.3.2 Release](https://github.com/pallets/flask/releases/tag/2.3.2) - [Flask 2.2.5 Release](https://github.com/pallets/flask/releases/tag/2.2.5)

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