Bug 2526729 (CVE-2026-84185)

Summary: CVE-2026-84185 jwcrypto: jwcrypto: General JSON JWS kid binding bypass during JWKSet verification
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: aprice, aruklets, doconnor, dschmidt, eglynn, jjoyce, jlanda, jpretori, jsamir, jschluet, jwong, kshier, lhh, mburns, mgarciac, oezr, omaciel, rhel-process-autobot, security-response-team, simaishi, stcannon, teagle, ttakamiy, watson-tool-maintainers, yguenane
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the jwcrypto library, which is used for implementing Javascript Object Signing and Encryption (JOSE) standards. The issue occurs when the library verifies a General JSON Serialization JWS using a set of keys. Due to a coding error, the library fails to correctly identify the specific key ID (kid) and may instead accept a signature made by any valid key in the set. This can allow an attacker with a valid key to bypass authorization checks in applications that rely on the key ID to identify specific tenants or users.
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Description OSIDB Bzimport 2026-09-01 10:33:37 UTC 
A flaw was found in jwcrypto. When verifying a General JSON Serialization JWS using a JWKSet, the library does not correctly apply the current signature kid header when selecting the verification key. The root cause is located in jwcrypto/jws.py, where the code incorrectly evaluates the jose_header as a dictionary when it is actually a list for General JSON JWS objects. Consequently, the library may iterate through every key in the supplied JWKSet and accept a signature made by a different key than the one identified by the kid header.

An attacker who possesses a valid signing key within the application's trusted JWKSet can exploit this flaw to bypass kid-based authorization bindings. This allows the attacker to perform actions such as impersonating other tenants, accessing unauthorized data, or escalating privileges in applications that rely on the kid claim for security decisions.