How severe is CVE-2026-33557?

CVE-2026-33557 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2026-33557 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (44th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-33557?

CVE-2026-33557 affects Apache Kafka. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-33557?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2026-33557 have an EU (EUVD) identifier?

Yes. CVE-2026-33557 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-23846.

When was CVE-2026-33557 published?

CVE-2026-33557 was published on 2026-04-20 and last updated on 2026-06-30.

CVE-2026-33557

CVE-2026-33557 is a critical-severity vulnerability in Apache Kafka with a CVSS 3.x base score of 9.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-1285.

Key facts

Severity: Critical (CVSS 3.x base score 9.1)
EPSS exploit prediction: 1% (44th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-23846
Weakness: CWE-1285
Affected product: Apache Kafka
Published: 2026-04-20
Last modified: 2026-06-30

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.

Frequently asked questions

What is 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.
How severe is CVE-2026-33557?: CVE-2026-33557 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2026-33557 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (44th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-33557?: CVE-2026-33557 affects Apache Kafka. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-33557?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
Does CVE-2026-33557 have an EU (EUVD) identifier?: Yes. CVE-2026-33557 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-23846.
When was CVE-2026-33557 published?: CVE-2026-33557 was published on 2026-04-20 and last updated on 2026-06-30.

References

Affected products (1)

cpe:2.3:a:apache:kafka:*:*:*:*:*:*:*:*

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