Critical [CVE-2026-33557] Apache Kafka: Missing JWT token validation in OAUTHBEARER authentication
This critical-severity Apache Software Foundation advisory covers CVE-2026-33557 affecting Apache Kafka.
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Summary
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. Since Kafka v4.1.2 and v4.2.0 and later, the issue is fixed and will correctly validate the JWT token.
- Apache Kafka 4.1.0 through 4.1.1
Official advisory · high-confidence parse· fetched 1 month ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 1 month ago·verify at source
Mitigation
The source record does not include mitigation steps. That is not a statement that no fix exists — read the vendor advisory below for the authoritative guidance.
Official advisory · high-confidence parse· fetched 1 month ago·verify at source
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