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.
References
- www.cve.org/CVERecord ↗
- nvd.nist.gov/vuln/detail/CVE-2026-33557 ↗
- kafka.apache.org/cve-list ↗
- lists.apache.org/thread/v57o00hm6yszdpdnvqx2ss4561yh953h ↗
- www.openwall.com/lists/oss-security/2026/04/17/2 ↗
- access.redhat.com/security/cve/CVE-2026-33557 ↗
- bugzilla.redhat.com/show_bug.cgi ↗
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33557.json ↗
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