Apache Kafka: Missing JWT token validation in OAUTHBEARER authentication
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.
describes (1)
Related CVEs.
| ID | severity | exploitable | ||
|---|---|---|---|---|
| CVE-2026-33557US | — | — | ||
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.se… | ||||
references
External citations — patches, advisories, analysis.
- http://www.openwall.com/lists/oss-security/2026/04/17/2DISCUSSION
- https://access.redhat.com/security/cve/CVE-2026-33557WEB
- https://bugzilla.redhat.com/show_bug.cgi?id=2459739WEB
- https://kafka.apache.org/cve-listADVISORY
- https://lists.apache.org/thread/v57o00hm6yszdpdnvqx2ss4561yh953hADVISORY
- https://nvd.nist.gov/vuln/detail/CVE-2026-33557WEB
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33557.jsonWEB
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