Improper Verification of Cryptographic Signature in pyjwt - #VU132100
Published: May 21, 2026
Vulnerability identifier: #VU132100
CSH Severity: Low
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Clear
CVE-ID: N/A
CWE-ID: CWE-347
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: jpadilla (José Padilla)
Affected software:
pyjwt
pyjwt
Detailed vulnerability description
The vulnerability allows a remote user to bypass algorithm policy enforcement.
The vulnerability exists due to improper verification of cryptographic signature in the PyJWK verification path when decoding JWTs with PyJWK or PyJWKClient-derived keys. A remote user can sign a token with a disallowed algorithm while advertising an allowed algorithm in the JWT header to bypass algorithm policy enforcement.
Exploitation requires control of a registered JWK or JWKS private key, such as in multi-tenant or federation-style trust models.
Remediation
Install security update from vendor's website.