CVE-2026-33557: apache software foundation apache kafka

Vulnerability summary

CVE-2026-33557 is a critical (CVSS 9.1) vulnerability in apache software foundation apache kafka. EPSS estimates a 0.93% chance of exploitation in the next 30 days, higher than 60% of scored vulnerabilities.

Timeline

1. 20-04-2026
   PublishedVulnerability first disclosed.
2. 15-07-2026
   Last modifiedVulnerability information updated.

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.

• CWE-1285Improper Validation of Specified Index, Position, or Offset in InputThe product receives input that is expected to specify an index, position, or offset into an indexable resource such as a buffer or file, but it does not validate or incorrectly validates that the specified index/position/offset has the required properties.
• CWE-303Incorrect Implementation of Authentication AlgorithmThe requirements for the product dictate the use of an established authentication algorithm, but the implementation of the algorithm is incorrect.