---
title: "CVE-2026-33557: Apache Kafka does not validate JWT tokens in its OAUTHBEARER authentication implementation"
url: https://erroneo.us/security/cve/CVE-2026-33557/
description: "CVE-2026-33557 (org.apache.kafka:kafka-clients (Maven)): A possible security vulnerability has been identified in Apache Kafka. By default, the broker…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-04-20
date_modified: 2026-07-15
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-33557"
kev: false
cvss: 8.6
epss: 0.00933
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-33557: Apache Kafka does not validate JWT tokens in its OAUTHBEARER authentication implementation

**Signal:** Normal patch cycle. No exploitation signal; fix it in your next routine update if you are affected. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.9% , percentile 60: FIRST’s model estimates a 0.9% chance of exploitation activity in the next 30 days, higher than 60% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes org.apache.kafka:kafka-clients (Maven) >= 4.1.0, < 4.1.2, fixed in 4.1.2 . Check your lockfile, including transitive dependencies.

## What it is

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 preferredusername 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

- Maven `org.apache.kafka:kafka-clients` >= 4.1.0, < 4.1.2 → fixed: 4.1.2

## Affected products (CVE record)

- Apache Software Foundation Apache Kafka: 4.1.0 <= 4.1.1

## Severity

- CISA-ADP CVSS 3.1: 9.1 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`
- redhat-SADP CVSS 3.1: 8.6 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L`
- GitHub CVSS 3.1: 9.1 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable yes , technical impact partial .
- FIRST EPSS (model of 2026-10-21): 0.93% probability of exploitation activity in the next 30 days; percentile 60.

## Sources

- [kafka.apache.org](https://kafka.apache.org/cve-list)
- [GitHub Advisory GHSA-28jg-cgg7-j4wc](https://github.com/advisories/GHSA-28jg-cgg7-j4wc)
- [CVE.org record CVE-2026-33557](https://www.cve.org/CVERecord?id=CVE-2026-33557)
- [NVD entry CVE-2026-33557](https://nvd.nist.gov/vuln/detail/CVE-2026-33557)
- [lists.apache.org](https://lists.apache.org/thread/v57o00hm6yszdpdnvqx2ss4561yh953h)
- [openwall.com](http://www.openwall.com/lists/oss-security/2026/04/17/2)
- [access.redhat.com](https://access.redhat.com/security/cve/CVE-2026-33557)
- [RHBZ#2459739](https://bugzilla.redhat.com/show_bug.cgi?id=2459739)
- [security.access.redhat.com](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33557.json)
- [github.com](https://github.com/apache/kafka/commit/01d8e7db8d08dbd538892b409457ea6bfcc2a422)

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Source page: https://erroneo.us/security/cve/CVE-2026-33557/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt