Improper Verification of Cryptographic Signature in pyjwt - #VU150530
Published: September 17, 2026
Vulnerability identifier: #VU150530
CSH Severity: Medium
CVSS v4: 9.1 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N]
CVE-ID: N/A
CWE-ID: CWE-347
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to forge authentication tokens with arbitrary claims.
The vulnerability exists due to improper verification of cryptographic signatures in HMACAlgorithm.from_jwk when resolving JWKs for HMAC signature verification. A remote attacker can submit a forged bearer token signed with an empty HMAC key to forge authentication tokens with arbitrary claims.
The issue is reachable when a trusted JWKS contains an oct entry whose k value is empty.
Affected software
pyjwt
Remediation
Install security update from vendor's website.
pyjwt - update to 2.14.0