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CVE-2026-33557 — Vulnerability in org.apache.kafka:kafka-clients —...

CRITICAL

Apache Kafka does not validate JWT tokens in its OAUTHBEARER authentication implementation

Published April 20, 2026Updated September 10, 2026Source: osv

Summary

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.

Advisory Timeline

  • First published April 20, 2026 (175 days ago).
  • Last revised September 10, 2026 — 143 days after initial publication.

Remediation

Upgrade to the fixed version using your package manager.

Maven
Update org.apache.kafka:kafka-clients to 4.1.2 or later
<!-- Update pom.xml dependency version to 4.1.2 for org.apache.kafka:kafka-clients -->

After upgrading, run your dependency scanner again to confirm the vulnerability is resolved.

Affected Packages (1)

Affects 1 ecosystem: maven (1).

PackageEcosystemAffectedFixed In
org.apache.kafka:kafka-clients
maven
4.1.0, 4.1.14.1.2

Vulnerability Classification

Common Weakness Enumeration (CWE) identifiers for this vulnerability type.

CVSS Score Breakdown

What the CVSS (Common Vulnerability Scoring System) 9.1 score means for each attack dimension.

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

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

References

Frequently Asked Questions

What is CVE-2026-33557?
Apache Kafka does not validate JWT tokens in its OAUTHBEARER authentication implementation This vulnerability has been assigned a severity rating of CRITICAL (CVSS score: 9.1/10).
How do I check if my project is affected by CVE-2026-33557?
CVE-2026-33557 affects org.apache.kafka:kafka-clients. Use GeekWala's free vulnerability scanner to check your dependencies against CVE-2026-33557 and 200,000+ other known vulnerabilities.

Severity & Exploitability

CVSS Score
9.1

Exploitation is straightforward and causes maximum impact. Patch immediately.

Also Known As

GHSA-28jg-cgg7-j4wc
BIT-kafka-2026-33557

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