Vulnerability record · CVE-2026-85394 · published 3 September 2026

CVE-2026-85394: Improper verification of cryptographic signature vulnerability

python-jose through 3.5.0 fails to properly validate asymmetric keys in HMAC initialization, accepting DER-encoded public keys that lack PEM armor or SSH prefixes. Attackers holding the service's public key can forge HS256 tokens that pass verification when algorithms are not explicitly restricted. This is an incomplete fix for CVE-2024-33663.

9.3 CVSS 4.0 Critical EPSS 0.35% · top 73.5% CWE-347 · Improper verification of cryptographic signature Deferred

9.3CVSS 4.0 base score

0.35%EPSS exploitation probability, 30 days

NoNot in CISA KEV

0Affected product versions listed by NVD

6References

24 Sep 2026Last modified by NVD

Description

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/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:

References

Link	Tags
https://github.com/advisories/GHSA-6c5p-j8vq-pqhj
https://github.com/mpdavis/python-jose
https://github.com/mpdavis/python-jose/blob/018b310ddb8b50dcfd09a0c152117835a21dd656/jose/backends/native.py
https://github.com/mpdavis/python-jose/blob/018b310ddb8b50dcfd09a0c152117835a21dd656/jose/utils.py
https://github.com/mpdavis/python-jose/issues/414
https://www.vulncheck.com/advisories/python-jose-through-3.5.0-algorithm-confusion-via-der-encoded-public-key-as-hmac-se

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-85394), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.