CVE-2026-33557: Kafka clients Apache Kafka Does Not Validate Vulnerability

CRITICAL
Advisory Identifier: GHSA-28jg-cgg7-j4wc
Share
CVSS 9.1
CWE-1285
Published
Advisory Summary

CVE-2026-33557 is a CRITICAL (CVSS 9.1) apache kafka does not validate vulnerability (CWE-1285: Improper Validation of Specified Index, Position, or Offset in Input) affecting Kafka clients libraries in the Maven ecosystem. The issue involves apache kafka does not validate jwt tokens in its oauthbearer authentication implementation. Remediation is available by upgrading affected packages to version 4.1.2.

CVE-2026-33557 at a Glance

CVE Identifier CVE-2026-33557
GHSA Identifier GHSA-28jg-cgg7-j4wc
Severity CRITICAL
CVSS v3.1 Base Score 9.1
CWE Classification CWE-1285: Improper Validation of Specified Index, Position, or Offset in Input
Affected Product Kafka clients
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 9.1

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity High (I:H)
Availability None (A:N)

How to Fix CVE-2026-33557

To remediate this vulnerability, upgrade all affected Kafka clients dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

org.apache.kafka:kafka-clients fixed: 4.1.2 
<dependency>
    <groupId>org.apache.kafka</groupId>
    <artifactId>kafka-clients</artifactId>
    <version>4.1.2</version>
</dependency>
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

mvn dependency:tree -Dincludes=org.apache.kafka

How to Check if You Are Affected

To determine whether your Java application is affected by CVE-2026-33557, inspect your build dependencies using the Maven Dependency Plugin:

mvn dependency:tree -Dincludes=org.apache.kafka

Analyze the terminal output to locate any version of Kafka clients in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.1.2), your application is affected.

Note: The mvn dependency:tree -Dincludes=org.apache.kafka command inspects the resolved dependency graph declared in your project's POM files; it does not perform automated security scanning or inspect runtime dynamic classpaths. Always verify runtime container classpaths and shaded JARs.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-1285: Improper Validation of Specified Index, Position, or Offset in Input, where the product receives input that is expected to specify an index, position, or offset into an indexable resource such as a buffer or file, but it does not validate or incorrectly validates that the specified index/position/offset has the required properties. In Kafka clients, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

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.

CVE-2026-33557 Affected Kafka clients Versions

1 component(s)
Fixed Versions:
4.1.2
Product / Package Ecosystem Affected Versions Fixed Version
org.apache.kafka:kafka-clients
maven/org.apache.kafka/kafka-clients
Maven
≥ 4.1.0
< 4.1.2
4.1.2

References

NVD — CVE-2026-33557 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-33557
Security Fix Commit FIX COMMIT
https://github.com/apache/kafka/commit/01d8e7db8d08dbd538892b409457ea6bfcc2a422
Kafka clients Source Repository REPOSITORY
https://github.com/apache/kafka
kafka.apache.org/cve-list WEB
https://kafka.apache.org/cve-list
lists.apache.org/thread/v57o00hm6ysz... WEB
https://lists.apache.org/thread/v57o00hm6yszdpdnvqx2ss4561yh953h
Kafka clients Security Information SECURITY
http://www.openwall.com/lists/oss-security/2026/04/17/2

Frequently Asked Questions

What is CVE-2026-33557?
CVE-2026-33557 is a security vulnerability in Kafka clients involving Apache Kafka does not validate JWT tokens in its OAUTHBEARER authentication implementation under CWE-1285: Improper Validation of Specified Index, Position, or Offset in Input.
Which Kafka clients versions are affected?
Affected versions include releases prior to 4.1.2 across affected packages: org.apache.kafka:kafka-clients.
What version fixes CVE-2026-33557?
Upgrading to 4.1.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is kafka-clients affected?
Yes, org.apache.kafka:kafka-clients is affected in releases prior to 4.1.2. Upgrade your dependency to 4.1.2 or later.
What is the CVSS score of CVE-2026-33557?
CVE-2026-33557 has a CVSS v3.1 base score of 9.1 (CRITICAL) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.
What CWE is associated with CVE-2026-33557?
CVE-2026-33557 is classified under CWE-1285: Improper Validation of Specified Index, Position, or Offset in Input (The product receives input that is expected to specify an index, position, or offset into an indexable resource such as a buffer or file, but it does not validate or incorrectly validates that the specified index/position/offset has the required properties.).
How can I check Maven dependencies for CVE-2026-33557?
Run the dependency tree command: 'mvn dependency:tree -Dincludes=org.apache.kafka'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-28jg-cgg7-j4wc",
  "modified" : "2026-04-24T15:29:32Z",
  "published" : "2026-04-20T15:31:52Z",
  "aliases" : [ "CVE-2026-33557" ],
  "summary" : "Apache Kafka does not validate JWT tokens in its OAUTHBEARER authentication implementation",
  "details" : "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.\n\nApache 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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.apache.kafka:kafka-clients"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.1.0"
      }, {
        "fixed" : "4.1.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-33557"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/apache/kafka/commit/01d8e7db8d08dbd538892b409457ea6bfcc2a422"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/apache/kafka"
  }, {
    "type" : "WEB",
    "url" : "https://kafka.apache.org/cve-list"
  }, {
    "type" : "WEB",
    "url" : "https://lists.apache.org/thread/v57o00hm6yszdpdnvqx2ss4561yh953h"
  }, {
    "type" : "WEB",
    "url" : "http://www.openwall.com/lists/oss-security/2026/04/17/2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1285" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-24T15:29:31Z",
    "nvd_published_at" : "2026-04-20T14:16:18Z"
  }
}