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.
History

Thu, 15 May 2025 04:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

cvssV3_1

{'score': 2.3, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L'}

threat_severity

Low


Tue, 13 May 2025 21:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Tue, 13 May 2025 16:15:00 +0000

Type Values Removed Values Added
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.
Title Flask uses fallback key instead of current signing key
Weaknesses CWE-683
References
Metrics cvssV4_0

{'score': 1.8, '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'}


cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published: 2025-05-13T15:57:40.409Z

Updated: 2025-05-13T20:14:09.702Z

Reserved: 2025-05-05T16:53:10.373Z

Link: CVE-2025-47278

cve-icon Vulnrichment

Updated: 2025-05-13T20:14:03.651Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2025-05-13T16:15:32.187

Modified: 2025-05-13T19:35:18.080

Link: CVE-2025-47278

cve-icon Redhat

Severity : Low

Publid Date: 2025-05-13T15:57:40Z

Links: CVE-2025-47278 - Bugzilla