High severity7.4NVD Advisory· Published Nov 2, 2026

CVE-2026-120459

Description

python-jose through 3.5.0 contains an authentication bypass vulnerability that allows unauthenticated attackers to forge JWTs because HMACKey and CryptographyHMACKey accept zero-length HMAC secrets. When an application's HS256/HS384/HS512 verification key resolves to empty, such as an oct JWK with empty k, attackers can forge tokens with arbitrary claims that jwt.decode accepts.

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Affected products

Python Jose Project/Python Josellm-fuzzy
Range: <=3.5.0
Mpdavis/python-josellm-fuzzy
Range: <=3.5.0

Patches

Vulnerability mechanics

References

github.com/mpdavis/python-jose/blob/3.5.0/jose/backends/cryptography_backend.pynvd
github.com/mpdavis/python-jose/blob/3.5.0/jose/backends/native.pynvd
github.com/mpdavis/python-jose/issues/398nvd
www.vulncheck.com/advisories/python-jose-through-3.5.0-authentication-bypass-via-empty-hmac-keynvd

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