CVE-2026-33557
CriticalCVSS 9.1Exploitation Probability (EPSS)
Low risk44th percentile - higher than 44% of all known CVEs
Summary
In Apache Kafka, the default JWT validator class (`DefaultJwtValidator`) accepts any JWT token without validating its signature, issuer, or audience. An attacker can generate a token from any issuer with any username, and the broker will accept it.
Risk Assessment
The organization is at risk of unauthorized access to the Kafka cluster – an attacker can impersonate any user, potentially leading to data confidentiality and integrity breaches.
Recommendation
Explicitly set the broker property `sasl.oauthbearer.jwt.validator.class` to `org.apache.kafka.common.security.oauthbearer.BrokerJwtValidator` on Kafka versions 4.1.0 and 4.1.1, or upgrade to version 4.1.2 or later.
Original NVD description (English source)
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.