CVE-2026-33557
CRITICAL9.1EPSS 0.22%Apache Kafka does not validate JWT tokens in its OAUTHBEARER authentication implementation
Description
A 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. Apache advises 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.
Affected packages (2)
- Bitnami/kafka>= 4.1.0, < 4.1.2
- Maven/org.apache.kafka:kafka-clients>= 4.1.0, < 4.1.2
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | CRITICAL9.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N |
References (6)
- ADVISORYhttps://nvd.nist.gov/vuln/detail/CVE-2026-33557
- PATCHhttps://github.com/apache/kafka
- WEBhttps://github.com/apache/kafka/commit/01d8e7db8d08dbd538892b409457ea6bfcc2a422
- WEBhttps://kafka.apache.org/cve-list
- WEBhttps://lists.apache.org/thread/v57o00hm6yszdpdnvqx2ss4561yh953h
- WEBhttp://www.openwall.com/lists/oss-security/2026/04/17/2