Vulnerability 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.
CVSS Score
CRITICAL
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Apache | Kafka | >= 4.1.0, < 4.1.2 |
Related Weaknesses (CWE)
References
- https://kafka.apache.org/cve-listVendor Advisory
- https://lists.apache.org/thread/v57o00hm6yszdpdnvqx2ss4561yh953hVendor AdvisoryMitigation
- http://www.openwall.com/lists/oss-security/2026/04/17/2Mailing List
FAQ
What is CVE-2026-33557?
CVE-2026-33557 is a vulnerability with a CVSS score of 9.1 (CRITICAL). 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.D...
How severe is CVE-2026-33557?
CVE-2026-33557 has been rated CRITICAL with a CVSS base score of 9.1/10. This is considered a critical vulnerability requiring immediate attention.
Is there a patch for CVE-2026-33557?
Check the references section above for vendor advisories and patch information. Affected products include: Apache Kafka.