Vulnerability · Published May 13, 2025 · Assigned by GitHub_M
CVE-2025-47278Flask uses fallback key instead of current signing key
Low 1.8
In plain English
A low-severity security flaw in flask from pallets. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 9% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:13 | flask | 3.1.1-1 | DEBIAN-CVE-2025-47278 |
| Debian:14 | flask | 3.1.1-1 | DEBIAN-CVE-2025-47278 |
| PyPI | flask | 3.1.1 | GHSA-4grg-w6v8-c28g |
| PyPI | flask | 3.1.1 | PYSEC-2026-1377 |
Affected products (as reported)
Weakness: CWE-683 · 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
References
- https://github.com/pallets/flask/security/advisories/GHSA-4grg-w6v8-c28g x_refsource_CONFIRM
- https://github.com/pallets/flask/commit/73d6504063bfa00666a92b07a28aaf906c532f09 x_refsource_MISC
- https://github.com/pallets/flask/releases/tag/3.1.1 x_refsource_MISC