Critical severity · published Sep 28, 2026
CVE-2026-102266
PyJWK accepts empty HMAC keys, bypassing PyJWT's empty-key validation
9.1
CVSS
0.2%
EPSS
No
On KEV
Description
PyJWT is a Python implementation of JSON Web Token standards. From 2.13.0 until 2.14.0, HMACAlgorithm.from_jwk is affected because PyJWK verification path used the decoded key without applying prepare_key validation. This occurs when a trusted JWK Set contains an oct entry with an empty k value. As a result, an attacker signs an HMAC token with the same zero-length key accepted by PyJWT. Consequently, forged token can carry arbitrary authenticated claims. This issue is fixed in version 2.14.0.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 13% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
PY
pyjwt · jpadilla
>= 2.13.0, < 2.14.0 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-102266
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-102266
x_refsource_CONFIRM
https://github.com/jpadilla/pyjwt/security/advisories/GHSA-9j54-fg26-wv3r
x_refsource_MISC
https://github.com/jpadilla/pyjwt/commit/f91ed44dd65baaf457f4b3353ed35e98a753934c
x_refsource_MISC
https://github.com/jpadilla/pyjwt/releases/tag/2.14.0
More from pyjwt
9.1
CVE-2026-102268
PyJWT: Asymmetric-PEM detection bypass: whitespace/line-ending-mutated public keys skip the HS/asymmetric confusion guard
9.1
CVE-2026-102267
PyJWT: PyJWKClient follows redirects when fetching JWKS
8.2
CVE-2026-102275
PyJWT accepts inconsistent OKP x/d JWKs, causing public/private key identity confusion
7.5
CVE-2026-102274
PyJWT: Malformed RSA JWK aborts parsing of an entire JWK Set
7.5
CVE-2026-101918
PyJWT: Unauthenticated RecursionError DoS in pre-verification payload parse (PyJWKClient.get_signing_key_from_jwt / verify_signature=False)