CVE-2026-33557
CRITICALCVE-2026-33557 is a critical-severity (CVSS 9.1) CWE-1285 vulnerability in org.apache.kafka:kafka-clients. O3 Security confirms whether CVE-2026-33557 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Apache Kafka: Missing JWT token validation in OAUTHBEARER authentication
Blast Radius
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 | 4.1.2 |
Detection & 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. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
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.
How O3 protects you
O3 pinpoints whether CVE-2026-33557 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-33557. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-33557 in your dependencies?
O3 detects CVE-2026-33557 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.