CVE-2026-33557

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.

The following products are affected by CVE-2026-33557 vulnerability.

Here, you will find a curated list of external links that provide in-depth information to CVE-2026-33557.

URL	Resource
http://www.openwall.com/lists/oss-security/2026/04/17/2
https://kafka.apache.org/cve-list
https://lists.apache.org/thread/v57o00hm6yszdpdnvqx2ss4561yh953h