CVE-2026-33557

Critical · CVSS 9.1

Apache Kafka — JWT authentication bypass via missing signature/issuer/audience validation (SASL OAuthBearer)

CVSS: 9.1; nvd
EPSS: —
KEV: No
Class: other; CWE-1285, CWE-303

Description

A possible security vulnerability has been identified in Apache Kafka. By default, the broker property `sasl.oauthbearer.jwt.validator.class` is set to `org.apache.kafka.common.security.oauthbearer.DefaultJwtValidator`. It accepts any JWT token without validating its signature, issuer, or audience. An attacker can generate a JWT token from any issuer with the `preferred_username` set to any user, and the broker will accept it. We advise the Kafka users using kafka v4.1.0 or v4.1.1 to set the config `sasl.oauthbearer.jwt.validator.class` to `org.apache.kafka.common.security.oauthbearer.BrokerJwtValidator` explicitly to avoid this vulnerability. Since Kafka v4.1.2 and v4.2.0 and later, the issue is fixed and will correctly validate the JWT token.

Search profile — drives PoC discovery

Symbols sasl.oauthbearer.jwt.validator.classorg.apache.kafka.common.security.oauthbearer.DefaultJwtValidatororg.apache.kafka.common.security.oauthbearer.BrokerJwtValidatorpreferred_usernamesasl.oauthbearerDefaultJwtValidatorBrokerJwtValidator

Keywords CVE-2026-33557Apache Kafka JWT bypassKafka OAuthBearer authentication bypassKafka DefaultJwtValidatorKafka BrokerJwtValidatorKafka SASL OAuthBearer JWT no signature validationKafka JWT token forgeCWE-1285 CWE-303 KafkaKafka 4.1.0 JWT vulnerabilityKafka 4.1.1 auth bypass

Versions: 4.1.0 - 4.1.1

References

Status: enriched · ingested 2026-06-30T06:00:22.000Z · profiled 2026-07-01T06:30:14.000Z