{"cve":"CVE-2025-47278","nvd":{"published":"2025-05-13T16:15:32.187","modified":"2026-06-17T09:27:39.367","status":"Deferred","description":"Flask is a web server gateway interface (WSGI) web application framework. In Flask 3.1.0, the way fallback key configuration was handled resulted in the last fallback key being used for signing, rather than the current signing key. Signing is provided by the `itsdangerous` library. A list of keys can be passed, and it expects the last (top) key in the list to be the most recent key, and uses that for signing. Flask was incorrectly constructing that list in reverse, passing the signing key first. Sites that have opted-in to use key rotation by setting `SECRET_KEY_FALLBACKS` care likely to unexpectedly be signing their sessions with stale keys, and their transition to fresher keys will be impeded. Sessions are still signed, so this would not cause any sort of data integrity loss. Version 3.1.1 contains a patch for the issue.","cvss_v4":{"vector":"CVSS:4.0/AV:L/AC:L/AT:P/PR:H/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N","score":1.8},"cvss_v3":null,"cwes":["CWE-683"],"references":["https://github.com/pallets/flask/commit/73d6504063bfa00666a92b07a28aaf906c532f09","https://github.com/pallets/flask/releases/tag/3.1.1","https://github.com/pallets/flask/security/advisories/GHSA-4grg-w6v8-c28g"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:01:22.920403922+00:00"},"epss":{"cve":"CVE-2025-47278","score":0.0019,"percentile":0.08681,"date":"2026-11-01"},"kev":null,"osv":[{"id":"GHSA-4grg-w6v8-c28g","url":"https://osv.dev/vulnerability/GHSA-4grg-w6v8-c28g","summary":"Flask uses fallback key instead of current signing key","modified":"2026-09-10T03:50:24.238504042Z","packages":[{"ecosystem":"PyPI","name":"flask","purl":"pkg:pypi/flask","ranges":[">=3.1.0 <3.1.1"],"fixed":["3.1.1"]}]},{"id":"PYSEC-2026-1377","url":"https://osv.dev/vulnerability/PYSEC-2026-1377","summary":"Flask uses fallback key instead of current signing key","modified":"2026-07-07T17:47:38.870624830Z","packages":[{"ecosystem":"PyPI","name":"flask","purl":"pkg:pypi/flask","ranges":[">=3.1.0 <3.1.1"],"fixed":["3.1.1"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}