What’s Vulnerable › Vulnerabilities

CVE-2026-33557: Apache Kafka: Missing JWT token validation in OAUTHBEARER authentication

• Severity: critical (CVSS 9.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.9% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-20 · updated 2026-10-26
• Weakness: CWE-1285

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.

Affected products

• Apache Kafka: from 4.1.0 before 4.1.2 — fixed in 4.1.2

How to fix

Upgrade to a fixed version: Apache Kafka 4.1.2. Check the vendor advisory for mitigations.

References

• https://kafka.apache.org/cve-list
• https://lists.apache.org/thread/v57o00hm6yszdpdnvqx2ss4561yh953h
• http://www.openwall.com/lists/oss-security/2026/04/17/2
• https://access.redhat.com/security/cve/CVE-2026-33557
• https://bugzilla.redhat.com/show_bug.cgi?id=2459739
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33557.json

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