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Fencer Vulns
low 1.8

CVE-2025-47278 json

Flask uses fallback key instead of current signing key

published 2025-05-13 17 mo ago modified 2026-09-10 59 d ago also EUVD-2025-14386 , GHSA-4grg-w6v8-c28g , PYSEC-2026-1377

cvss
1.8
version 4.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 8%
public exploits
0
none known

Summary

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.

Patch / fix

  • pypi flask 3.1.1
  • palletsprojects flask 3.1.1
  • flask Debian 14, Debian 13 3.1.1-1

debian advisories DEBIAN-CVE-2025-47278

  • python-Flask openSUSE Tumbleweed 3.1.1-1.1

opensuse advisories openSUSE-SU-2025:15152-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2025-47278 updated cvss 2.3

flask: Flask Session Signing Fallback Key Vulnerability

  • Red Hat Enterprise Linux 8 python3-flask Red Hat OpenShift Container Platform 4 python-flask, python3-flask Red Hat OpenStack Platform 16.2 python-flask, python3-flask Red Hat OpenStack Platform 17.1 python3-flask Red Hat OpenStack Platform 18.0 python-flask Red Hat Quay 3 quay/quay-rhel8
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
17 mo ago

Exploit prediction

0.19% chance of exploitation in the next 30 days, higher than 8% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 1.8 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
CNA 4.0 1.8 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected packages

ecosystem package affected fixed in
pypi flask
>=3.1.0, <3.1.1
3.1.1

Affected products

  • pallets flask

Classification

Weakness
  • CWE-683 Function Call With Incorrect Order of Arguments
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

The maintainers of pallets/flask published their own advisory on GitHub. Reviewed sources take precedence over it.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.