CVE-2026-33557

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.

CVSS 3.1

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

EPSS

0.9% chance of exploitation in the next 30 days; higher than 59% of CVEs (scores of 2026-10-26)

CWEs

CWE-1285, CWE-303

Published

2026-04-20

Modified

2026-10-26

Record from

the NVD, synced 2026-10-26

Affected

• apache:kafka

Packages (OSV)

References

• https://kafka.apache.org/cve-list
• https://lists.apache.org/thread/v57o00hm6yszdpdnvqx2ss4561yh953h
• http://www.openwall.com/lists/oss-security/2026/04/17/2
• https://access.redhat.com/security/cve/CVE-2026-33557
• https://bugzilla.redhat.com/show_bug.cgi?id=2459739

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