CVE-2026-85394 python-jose through 3.5.0 Algorithm Confusion via DER-encoded Public Key as HMAC Secret
Attackers can forge JWT tokens by exploiting algorithm confusion in python-jose when asymmetric keys are used as HMAC secrets without explicit algorithm restrictions.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-85394?
CVE-2026-85394 is a critical vulnerability in mpdavis python-jose, published on 3 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-347
Which versions are affected by CVE-2026-85394?
How do I fix CVE-2026-85394?
Upgrade to a fixed version.
Is CVE-2026-85394 being exploited?
There is no known exploitation of CVE-2026-85394 in the wild and no public exploit code.
Sources
Also known as CLSA-2026-1791441237, ROOT-APP-PYPI-CVE-2026-85394, UBUNTU-CVE-2026-85394.