Improper Verification of Cryptographic Signature in pyjwt - #VU150522
Published: September 17, 2026
Vulnerability identifier: #VU150522
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 bypass authentication.
The vulnerability exists due to improper verification of cryptographic signatures in PyJWK HMAC key verification when verifying HS256 tokens using an empty oct JWK. A remote attacker can generate a forged HS256 JWT signed with the zero-length HMAC key to bypass authentication.
The application must already load an empty symmetric oct JWK, and minimum HMAC key-length enforcement must be disabled.
Affected software
pyjwt
Remediation
Install security update from vendor's website.
pyjwt - update to 2.14.0