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Status

Current state: "Under Discussion"

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Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

Apache Kafka is increasingly used in environments where security is critical. TLS can be used a security protocol with Kafka to enable server authentication, client authentication and encryption. Even though Kafka supports server hostname verification and the documentation talks about setting hostnames in server certificates, hostname verification is disabled by default. This in an insecure default value since hostname verification is required to prevent man-in-the-middle attacks.

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This KIP proposes to enable hostname verification by default for Kafka client connections to prevent man-in-the-middle attacks.

Public Interfaces

The default value of ssl.endpoint.identification.algorithm will be changed to HTTPS. Hostname verification can be disabled if required by setting the config to an empty string. The default will apply to both client configs (producer/consumer/admin client etc.) and inter-broker connections. The config can be set at listener-level.

Proposed Changes

This will be a simple change of the default value of ssl.endpoint.identification.algorithm to HTTPS. Any tests that rely on this config to be disabled will be updated to explicitly set the config to an empty string. Any test which doesn't care about the value of this config, but generates certificates without hostnames will be updated to set hostnames in certificates. All system tests are currently run wth ssl.endpoint.identification.algorithm=HTTPS anyway, so no changes are required.

Compatibility, Deprecation, and Migration Plan

Even though hostname verification should be enabled to protect against man-in-the-middle attacks, there may be environments where certificates are generated without hostnames and endpoint identification is performed in other ways. It is possible that some of these installations are currently using the default config. They will need to explicitly set ssl.endpoint.identification.algorithm to an empty string when upgrading. This will be documented in upgrade notes.

Rejected Alternatives

Disable hostname verification for SASL_SSL with Kerberos by default

Kerberos performs hostname verification, so we could leave default value as-is, i.e. disabled for client connections with SASL_SSL using GSSAPI as the mechanism. But it is safer to use the same default value for TLS across all security protocols and SASL mechanisms. Hence this KIP proposes to simply use a secure default, leaving it up to the user to disable if required.

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