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Vulnerability · Published Apr 20, 2026 · Assigned by apache

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

Critical 9.1

In plain English

A critical-severity security flaw in Apache Kafka from Apache Software Foundation. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.9% (higher than 60% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)9.1Critical
Exploit odds (30 days)0.9%top 40.2% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official 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 packages & fixed versions

EcosystemPackageFixed inAdvisory
Mavenorg.apache.kafka:kafka-clients4.1.2GHSA-28jg-cgg7-j4wc

Affected products (as reported)

VendorProductVersions
Apache Software Foundation Apache Kafka 4.1.0 – through 4.1.1

Weakness: CWE-1285, CWE-303 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

References