What’s Vulnerable › Vulnerabilities

CVE-2026-85394: python-jose through 3.5.0 Algorithm Confusion via DER-encoded Public Key as HMAC Secret

• Severity: critical (CVSS 9.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-03 · updated 2026-09-24
• Weakness: CWE-347

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.

Affected products

• mpdavis python-jose: through 3.5.0

References

• 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-secret

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