Bug 2459739 (CVE-2026-33557) - CVE-2026-33557 kafka: Apache Kafka: Authentication bypass via improper JWT validation
Summary: CVE-2026-33557 kafka: Apache Kafka: Authentication bypass via improper JWT va...
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Status: NEW
Alias: CVE-2026-33557
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
high
high
Target Milestone: ---
Assignee: Product Security
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Blocks:
TreeView+ depends on / blocked
 
Reported: 2026-04-20 14:01 UTC by OSIDB Bzimport
Modified: 2026-04-23 18:11 UTC (History)
75 users (show)

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Description OSIDB Bzimport 2026-04-20 14:01:31 UTC 
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.
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