CVE-2026-33557
Apache Kafka: Missing JWT token validation in OAUTHBEARER authentication
- State
- Published
- Severity
- 9.1 Critical
- Published
- Apr 20, 2026
- Updated
- Jul 15, 2026
- Reserved
- Mar 23, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 3.1 | 9.1 Critical | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N | CISA-ADP |
| 3.1 | 8.6 High | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L | redhat-SADP |
Weaknesses
Affected Products
| Product | Versions |
|---|---|
Apache KafkaApache Software Foundation |
|
References
- https://kafka.apache.org/cve-listvendor-advisory
- https://lists.apache.org/thread/v57o00hm6yszdpdnvqx2ss4561yh953hmailing-list
- http://www.openwall.com/lists/oss-security/2026/04/17/2
- https://access.redhat.com/security/cve/CVE-2026-33557vdb-entry
- RHBZ#2459739issue-tracking
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33557.json
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