{"id":"UBUNTU-CVE-2026-33557","details":"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.","modified":"2026-06-30T18:17:55.695237312Z","published":"2026-04-20T14:16:00Z","upstream":["CVE-2026-33557"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-33557"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-33557"}],"affected":[{"package":{"name":"kafka","ecosystem":"Ubuntu:Pro:18.04:LTS","purl":"pkg:deb/ubuntu/kafka?arch=source&distro=esm-apps%2Fbionic"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.2.0u2-0ubuntu3.1","2.2.0u2-0ubuntu3.2","2.2.2u1-0ubuntu1+esm2"],"ecosystem_specific":{"binaries":[{"binary_name":"kafka","binary_version":"2.2.2u1-0ubuntu1+esm2"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-33557.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N"},{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L"},{"type":"Ubuntu","score":"medium"}]}