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Low severityOSV Advisory· Published May 13, 2025· Updated Apr 15, 2026

CVE-2025-47278

CVE-2025-47278

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.

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Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
flaskPyPI
>= 3.1.0, < 3.1.13.1.1

Affected products

47

Patches

Vulnerability mechanics

References

5

News mentions

0

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