CVE-2026-33557

Summary

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 Software

Weaknesses

• CWE-1285: CWE-1285 Improper Validation of Specified Index, Position, or Offset in Input

ADP Enrichment

CVE Program Container

Additional References

• http://www.openwall.com/lists/oss-security/2026/04/17/2

CISA ADP Vulnrichment

• SSVC:
• Exploitation: none
  • Automatable: yes
  • Technical Impact: partial

kafka: Apache Kafka: Authentication bypass via improper JWT validation

Additional References

• https://access.redhat.com/security/cve/CVE-2026-33557
• https://bugzilla.redhat.com/show_bug.cgi?id=2459739
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33557.json

References

• https://kafka.apache.org/cve-list
• https://lists.apache.org/thread/v57o00hm6yszdpdnvqx2ss4561yh953h

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