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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-33557: 0.90% estimated exploitation activity in the next 30 days; percentile 59.64 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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 preferredusername 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.

Published by the source

20 Apr 2026, 15:31 UTC

Last modified by the source

24 Apr 2026, 15:29 UTC

Source last checked

26 Oct 2026, 16:45 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-28jg-cgg7-j4wc

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# Patch Next advisory brief: CVE-2026-33557

Advisory: Apache Kafka does not validate JWT tokens in its OAUTHBEARER authentication implementation
IDs: CVE-2026-33557, GHSA-28jg-cgg7-j4wc
Record: https://patchnext.com/advisories/cve-2026-33557 (revision 1, source checked 26 Oct 2026, 16:45 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: org.apache.kafka:kafka-clients 4.1.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven org.apache.kafka:kafka-clients: affected >= 4.1.0, < 4.1.2; fixed in 4.1.2

## Suggested inspection (read-only)
- Maven org.apache.kafka:kafka-clients: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on org.apache.kafka:kafka-clients.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-28jg-cgg7-j4wc (GitHub-reviewed advisory GHSA-28jg-cgg7-j4wc lists affected ranges: Maven org.apache.kafka:kafka-clients >=4.1.0 <4.1.2)

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