GHSA-m2qf-hxjv-5gpq

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    GHSA-m2qf-hxjv-5gpq

    Published: 1 May 2023Last Modified: 10 Sept 2026

    Summary: Flask vulnerable to possible disclosure of permanent session cookie due to missing Vary: Cookie header

    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`](https://flask.palletsprojects.com/en/2.3.x/api/#flask.session.permanent). 2. The application does not access or modify the session at any point during a request. 4. [`SESSION_REFRESH_EACH_REQUEST`](https://flask.palletsprojects.com/en/2.3.x/config/#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.

    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

    Affected packages

    Package

    Name: flask

    Purl: pkg:pypi/flask

    Affected ranges

    Type: ECOSYSTEM

    Events:

    Introduced- 2.3.0
    Fixed -2.3.2

    Affected versions

    2.3.0
    2.3.1

    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High
    GHSA-m2qf-hxjv-5gpq | CVE-DB