Vulnerability · Published Nov 2, 2026 · Assigned by VulnCheck

CVE-2026-120459python-jose through 3.5.0 Authentication Bypass via Empty HMAC Key

High 7.4

In plain English

A high-severity security flaw in python-jose from mpdavis. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 17% of all known vulnerabilities).

Severity (CVSS 3.1)7.4High

Exploit odds (30 days)0.3%top 83.4% of all CVEs

Exploited in the wildNo reportsnot in CISA KEV

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Ubuntu:22.04:LTS	python-jose	no fix listed	UBUNTU-CVE-2026-120459
Ubuntu:24.04:LTS	python-jose	no fix listed	UBUNTU-CVE-2026-120459

Affected products (as reported)

Vendor	Product	Versions
mpdavis	python-jose	0 – through 3.5.0

Weakness: CWE-347 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

References

https://github.com/mpdavis/python-jose/issues/398 issue-tracking
https://github.com/mpdavis/python-jose/blob/3.5.0/jose/backends/native.py technical-description
https://github.com/mpdavis/python-jose/blob/3.5.0/jose/backends/cryptography_backend.py technical-description
VulnCheck Advisory: python-jose through 3.5.0 Authentication Bypass via Empty HMAC Key third-party-advisory