CVE-2026-110985

A Kafka broker using SASL/OAUTHBEARER with the default validator (sasl.oauthbearer.jwt.validator.class=DefaultJwtValidator) selects its implementation from configuration. When sasl.oauthbearer.jwks.endpoint.url is set, the validator verifies the JWT signature. When that URL is unset (the default) and no verification key resolver is supplied, DefaultJwtValidator silently falls back to ClientJwtValidator, which does not verify the JWT signature, algorithm, or issuer - and the broker starts with no warning or error. This is the residual of CVE-2026-33557, whose fix restored signature verification only on the path where the JWKS endpoint URL is set. Impact: A broker in this state accepts any structurally valid JWT, including "alg":"none" tokens. An unauthenticated remote attacker who can reach the listener can forge a token asserting any principal - including configured superusers - and gain full access to the cluster. Only brokers that enable SASL/OAUTHBEARER validation without a JWKS endpoint URL (and without a custom verification key resolver) are affected; brokers that set the URL verify signatures and are not affected. Unlike CVE-2026-110952 (issuer/audience not enforced by default), here no signature is verified at all. Mitigation (all affected versions, no upgrade required): Set sasl.oauthbearer.jwks.endpoint.url for every listener/mechanism that uses OAuthBearerValidatorCallbackHandler, or configure a signature-verifying sasl.oauthbearer.jwt.validator.class. Resolution: From Apache Kafka 4.2.2, 4.3.1, and 4.4.0: a broker that would fall back to the non-verifying ClientJwtValidator fails to start with a ConfigException instead of running without signature verification (secure by default).

CVSS

No CVSS.

References

Link	Resource
https://kafka.apache.org/cve-list

Configurations

No configuration.

History

28 Oct 2026, 17:17

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-10-28 17:17

Updated : 2026-10-29 15:04

NVD link : CVE-2026-110985

Mitre link : CVE-2026-110985

CVE.ORG link : CVE-2026-110985

JSON object : View

Products Affected

No product.

CWE

CWE-345

Insufficient Verification of Data Authenticity

CWE-347

Improper Verification of Cryptographic Signature

CWE-636

Not Failing Securely ('Failing Open')

CWE-1287

Improper Validation of Specified Type of Input

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