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CVE-2026-33557

CriticalPublished

Apache Kafka: Missing JWT token validation in OAUTHBEARER authentication

Published: Apr 20, 2026
Updated: Jul 15, 2026
Assigning CNA: apache
Evidence observed: Aug 30, 2026

Primary CVSS

9.1/ 10Critical

nvd · CVSS 3.1

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS probability estimate

0.7%

Low · next 30 days

Percentile: 50.7%
Model date: Sep 21, 2026

EPSS is a statistical estimate, not a certainty or a measure of impact. Combine it with CVSS, KEV status, exposure and your environment.

Summary

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.

Sources

vulnerability-pocPoC
CVE proof-of-concept labs, exploit scripts, and detection/prevention rules (Nginx, Apache, Snort, YARA) for high-severity CVEs. Authorized security testing & research only.

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