CVE-2026-33557 is a critical-severity (CVSS 9.1) CWE-1285 vulnerability in org.apache.kafka:kafka-clients. A fix is available for org.apache.kafka:kafka-clients — see the affected versions and patch details below.
Apache Kafka: Missing JWT token validation in OAUTHBEARER authentication
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-33557.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
org.apache.kafka:kafka-clientsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.apache.kafka:kafka-clients | ≥ 4.1.0&&< 4.1.2 | 4.1.2org.apache.kafka:kafka-clients:4.1.2 |
Affected Products
kafkaapacheDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.kafka:kafka-clients, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update org.apache.kafka:kafka-clients to 4.1.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-33557 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2026-33557 in your dependencies?
Find it across Maven, including transitive dependencies.