Live › vulnerability › CVE-2026-110985
Go to dashboardA Kafka broker using SASL/OAUTHBEARER with the default validator and no JWKS endpoint URL silently falls back to a validator that checks no JWT signature, algorithm or issuer. An unauthenticated remote attacker who can reach the listener can forge a token for any principal, including configured superusers, and gain full cluster access.
Summary written from the sources below. Check the originals before acting.
First seen by InfraStack 2026-10-28 17:34 UTC. All times on this page are UTC.
Brokers that enable SASL/OAUTHBEARER validation with the default DefaultJwtValidator and leave sasl.oauthbearer.jwks.endpoint.url unset, without a custom verification key resolver, are affected. Brokers that set the JWKS URL verify signatures and are not affected. Teams running Kafka with SASL/OAUTHBEARER on any listener should check every listener.
No product ranges from the sources yet.
sasl.oauthbearer.jwt.validator.class and sasl.oauthbearer.jwks.endpoint.url; if the URL is unset and no signature-verifying validator or verification key resolver is configured, the broker is exposedkafka-topics.sh --version or the broker's kafka_*.jar version; versions before 4.2.2, 4.3.1 and 4.4.0 are in scope per the sourcessasl.oauthbearer.jwks.endpoint.url for every listener and mechanism that uses OAuthBearerValidatorCallbackHandlersasl.oauthbearer.jwt.validator.class4.2.2, 4.3.1 or 4.4.0, where a broker that would fall back fails to start insteadEach row is the first time that source carried this signal. The analyst’s rows are its own findings.
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).
This page as .md · .json · in your agent: get_signal("CVE-2026-110985")
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