CVE-2026-33557
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.
How to fix
- apache kafka4.1.2 or later
- org.apache.kafka:kafka-clients4.1.2 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| apache kafka | 4.1.0 ≤ v < 4.1.2 | 4.1.2 |
| org.apache.kafka:kafka-clientsMaven | 4.1.0 ≤ v < 4.1.2 | 4.1.2 |
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