Vulnerability details

CVE-2026-85394

mpdavis python-jose

python-jose through 3.5.0 Algorithm Confusion via DER-encoded Public Key as HMAC Secret

CVSS 4.0

9.3Critical

Official description

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.

CVSS scores

Score	Version	Source	Vector
9.3Critical	4.0	CVEProject cvelistV5 (CNA) (VulnCheck)	`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`
9.1Critical	3.1	CVEProject cvelistV5 (CNA) (VulnCheck)	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`

Affected products

Vendor	Product	Versions	Source
mpdavis	python-jose	v ≤ 3.5.0	CVEProject cvelistV5 (CNA)

References and advisories

https://github.com/mpdavis/python-jose/issues/414 issue-tracking
https://github.com/mpdavis/python-jose product
https://github.com/mpdavis/python-jose/blob/018b310ddb8b50dcfd09a0c152117835a21dd656/jose/backends/native.py technical-description
https://github.com/mpdavis/python-jose/blob/018b310ddb8b50dcfd09a0c152117835a21dd656/jose/utils.py technical-description
https://github.com/advisories/GHSA-6c5p-j8vq-pqhj related
https://www.vulncheck.com/advisories/python-jose-through-3.5.0-algorithm-confusion-via-der-encoded-public-key-as-hmac-secret third-party-advisory

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Details

Published: 2026-09-03
Last updated: 2026-09-14
State: Published
Assigner (CNA): VulnCheck

Exploit prediction (EPSS)

0.22%

Probability of exploitation in 30 days

12.9%

Percentile (among all CVEs)

SSVC assessment (CISA)

Automatable: No
Exploitation: None
Technical impact: Total

Weaknesses (CWE)

CWE-347
Improper Verification of Cryptographic Signature