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CVE-2026-33557

Apache Kafka vulnerability

9.1 CRITICALEPSS 0.93%
  1. Published20 Apr 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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected products

Apache Kafka≥ 4.1.0 < 4.1.2

Remediation

Fixed in
Apache Kafka≥ 4.1.2

References

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Frequently asked

Is CVE-2026-33557 being actively exploited?

CVE-2026-33557 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.93%.

How severe is CVE-2026-33557?

CVE-2026-33557 has a CVSS 3.1 base score of 9.1, rated critical. EPSS estimates a 0.93% probability of exploitation.

Which products are affected by CVE-2026-33557?

Affected products include Apache Kafka.

How do I fix CVE-2026-33557?

Upgrade affected software to a fixed version, for example Apache Kafka 4.1.2 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-33557 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.