Vulnerability in Apache Kafka
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.
EPSS exploit prediction
EPSS: 0.009 (60.0th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 60th percentile — 60.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.007 · newest: 0.009 · change: +0.002
Affected products
- Apache Kafka
- Apache Software Foundation Kafka — versions 4.1.0
Weakness classification (CWE)
References
- kafka.apache.org/cve-list (vendor-advisory, Vendor Advisory)
- lists.apache.org/thread/v57o00hm6yszdpdnvqx2ss4561yh953h (Vendor Advisory, mailing-list, Mitigation)
- af854a3a-2127-422b-91ae-364da2661108 (Mailing List)
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
Frequently asked questions
- What is CVE-2026-33557?
- CVE-2026-33557 is a critical-severity vulnerability in Apache Kafka, classified under CWE-1285. CVSS score: 9.1/10. Published 2026-04-20.
- How severe is CVE-2026-33557?
- Critical severity. CVSS v3 base score is 9.1 out of 10.