{"id":"GHSA-m2qf-hxjv-5gpq","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.\n\n1. The application must be hosted behind a caching proxy that does not strip cookies or ignore responses with cookies.\n2. The application sets [`session.permanent = True`](https://flask.palletsprojects.com/en/2.3.x/api/#flask.session.permanent).\n2. The application does not access or modify the session at any point during a request.\n4. [`SESSION_REFRESH_EACH_REQUEST`](https://flask.palletsprojects.com/en/2.3.x/config/#SESSION_REFRESH_EACH_REQUEST) is enabled (the default).\n5. The application does not set a `Cache-Control` header to indicate that a page is private or should not be cached.\n\nThis 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.","aliases":["CVE-2023-30861","PYSEC-2023-62"],"modified":"2026-03-11T07:49:38.453892Z","published":"2023-05-01T19:22:20Z","database_specific":{"nvd_published_at":"2023-05-02T18:15:52Z","cwe_ids":["CWE-539"],"severity":"HIGH","github_reviewed":true,"github_reviewed_at":"2023-05-01T19:22:20Z"},"references":[{"type":"WEB","url":"https://github.com/pallets/flask/security/advisories/GHSA-m2qf-hxjv-5gpq"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2023-30861"},{"type":"WEB","url":"https://github.com/pallets/flask/commit/70f906c51ce49c485f1d355703e9cc3386b1cc2b"},{"type":"WEB","url":"https://github.com/pallets/flask/commit/afd63b16170b7c047f5758eb910c416511e9c965"},{"type":"PACKAGE","url":"https://github.com/pallets/flask"},{"type":"WEB","url":"https://github.com/pallets/flask/releases/tag/2.2.5"},{"type":"WEB","url":"https://github.com/pallets/flask/releases/tag/2.3.2"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/flask/PYSEC-2023-62.yaml"},{"type":"WEB","url":"https://lists.debian.org/debian-lts-announce/2023/08/msg00024.html"},{"type":"WEB","url":"https://security.netapp.com/advisory/ntap-20230818-0006"},{"type":"WEB","url":"https://www.debian.org/security/2023/dsa-5442"}],"affected":[{"package":{"name":"flask","ecosystem":"PyPI","purl":"pkg:pypi/flask"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.3.0"},{"fixed":"2.3.2"}]}],"versions":["2.3.0","2.3.1"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2023/05/GHSA-m2qf-hxjv-5gpq/GHSA-m2qf-hxjv-5gpq.json"}},{"package":{"name":"flask","ecosystem":"PyPI","purl":"pkg:pypi/flask"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.2.5"}]}],"versions":["0.1","0.10","0.10.1","0.11","0.11.1","0.12","0.12.1","0.12.2","0.12.3","0.12.4","0.12.5","0.2","0.3","0.3.1","0.4","0.5","0.5.1","0.5.2","0.6","0.6.1","0.7","0.7.1","0.7.2","0.8","0.8.1","0.9","1.0","1.0.1","1.0.2","1.0.3","1.0.4","1.1.0","1.1.1","1.1.2","1.1.3","1.1.4","2.0.0","2.0.0rc1","2.0.0rc2","2.0.1","2.0.2","2.0.3","2.1.0","2.1.1","2.1.2","2.1.3","2.2.0","2.2.1","2.2.2","2.2.3","2.2.4"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2023/05/GHSA-m2qf-hxjv-5gpq/GHSA-m2qf-hxjv-5gpq.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N"},{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N"}]}