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.
Other vulnerabilities in Apache Kafka
See all- CVE-2026-41115Medium
An improper authorization vulnerability has been identified in Apache Kafka. The CONSUMER_GROUP_DESCRIBE (69) API validates the DESCRIBE operation on the GROUP resource instead of the READ operation as documented. This can result in misconfigured ACLs and unintended security postures.
- CVE-2026-35554High
A race condition in the Apache Kafka Java producer client's buffer pool management can cause messages to be silently delivered to incorrect topics. The issue is fixed in newer versions.
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS