CVE-2026-33557

Published Apr 20, 2026

Last updated 3 months ago

CVSS critical 9.1
Apache Kafka
Kafka

Overview

AI description

Automated description summarized from trusted sources.

CVE-2026-33557 describes an authentication bypass vulnerability found in Apache Kafka. The flaw stems from the default configuration of the `sasl.oauthbearer.jwt.validator.class` property, which is set to `org.apache.kafka.common.security.oauthbearer.DefaultJwtValidator`. This default validator fails to properly validate JSON Web Token (JWT) signatures, issuers, or audiences. As a result, a remote attacker can exploit this weakness by crafting a malicious JWT token containing an arbitrary `preferred_username`. This allows the attacker to bypass authentication and gain unauthorized access to the Kafka broker. Apache Kafka versions 4.1.0 and 4.1.1 are affected, with the issue resolved in versions 4.1.2, 4.2.0, and later, which correctly validate JWT tokens. A recommended workaround for affected versions is to explicitly configure `sasl.oauthbearer.jwt.validator.class` to `org.apache.kafka.common.security.oauthbearer.BrokerJwtValidator`.

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.
Source
security@apache.org
NVD status
Modified
Products
kafka

Risk scores

CVSS 3.1

Type
Secondary
Base score
9.1
Impact score
5.2
Exploitability score
3.9
Vector string
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Severity
CRITICAL

Weaknesses

security@apache.org
CWE-1285
0b0ca135-0b70-47e7-9f44-1890c2a1c46c
CWE-303

Social media

Hype score
Not currently trending

  1. 🚨 CVE-2026-33557: Apache Kafka: Missing JWT token validation in OAUTHBEARER authentication Critical Vulnerability Alert! Kafka is affected by CVE-2026-33557. Full Vulnerability Details & Analysis at DarkEye: 🔗 https://t.co/aqNp4FRJM4 🔍 Identify Targets via ZoomEye

    @zoomeye_team

    13 Jul 2026

    1559 Impressions

    8 Retweets

    14 Likes

    1 Bookmark

    0 Replies

    0 Quotes

Configurations

Related CVEs

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References

Sources include official advisories and independent security research.