CVE-2026-33558: Apache Kafka, Apache Kafka Clients: Information Exposure Through Network Client Log Output

[Luke Chen <showuon () apache org>]

Severity: moderate 

Affected versions:

- Apache Kafka 0.11.0 through 3.9.1
- Apache Kafka 4.0.0
- Apache Kafka Clients (org.apache.kafka:kafka-clients) 0.11.0 through 3.9.1
- Apache Kafka Clients (org.apache.kafka:kafka-clients) 4.0.0

Description:

Information exposure vulnerability has been identified in Apache Kafka.

The NetworkClient component will output entire requests and responses information in the DEBUG log level in the logs. 
By default, the log level is set to INFO level. If the DEBUG level is enabled, the sensitive information will be 
exposed via the requests and responses output log. The entire lists of impacted requests and responses are:


  *  AlterConfigsRequest

  *  AlterUserScramCredentialsRequest

  *  ExpireDelegationTokenRequest

  *  IncrementalAlterConfigsRequest

  *  RenewDelegationTokenRequest

  *  SaslAuthenticateRequest

  *  createDelegationTokenResponse

  *  describeDelegationTokenResponse

  *  SaslAuthenticateResponse


This issue affects Apache Kafka: from any version supported the listed API above through v3.9.1, v4.0.0. We advise the 
Kafka users to upgrade to v3.9.2, v4.0.1, or later to avoid this vulnerability.

Credit:

Alyssa Huang <ahuang () confluent io> (finder)
Luke Chen <showuon () gmail com> (finder)

References:

https://kafka.apache.org/
https://www.cve.org/CVERecord?id=CVE-2026-33558