Files or Directories Accessible to External Parties, Improper Privilege Management vulnerability in Apache Kafka Clients.

Apache Kafka Clients accept configuration data for customizing behavior, and includes ConfigProvider plugins in order to manipulate these configurations. Apache Kafka also provides FileConfigProvider, DirectoryConfigProvider, and EnvVarConfigProvider implementations which include the ability to read from disk or environment variables. In applications where Apache Kafka Clients configurations can be specified by an untrusted party, attackers may use these ConfigProviders to read arbitrary contents of the disk and environment variables.

In particular, this flaw may be used in Apache Kafka Connect to escalate from REST API access to filesystem/environment access, which may be undesirable in certain environments, including SaaS products. This issue affects Apache Kafka Clients: from 2.3.0 through 3.5.2, 3.6.2, 3.7.0.

Users with affected applications are recommended to upgrade kafka-clients to version >=3.8.0, and set the JVM system property "org.apache.kafka.automatic.config.providers=none". Users of Kafka Connect with one of the listed ConfigProvider implementations specified in their worker config are also recommended to add appropriate "allowlist.pattern" and "allowed.paths" to restrict their operation to appropriate bounds.

For users of Kafka Clients or Kafka Connect in environments that trust users with disk and environment variable access, it is not recommended to set the system property. For users of the Kafka Broker, Kafka MirrorMaker 2.0, Kafka Streams, and Kafka command-line tools, it is not recommended to set the system property.

A possible security vulnerability has been identified in Apache Kafka. This requires access to a alterConfig to the cluster resource, or Kafka Connect worker, and the ability to create/modify connectors on it with an arbitrary Kafka client SASL JAAS config and a SASL-based security protocol, which has been possible on Kafka clusters since Apache Kafka 2.0.0 (Kafka Connect 2.3.0). When configuring the broker via config file or AlterConfig command, or connector via the Kafka Kafka Connect REST API, an authenticated operator can set the sasl.jaas.config property for any of the connector's Kafka clients to "com.sun.security.auth.module.LdapLoginModule", which can be done via the producer.override.sasl.jaas.config, consumer.override.sasl.jaas.config, or admin.override.sasl.jaas.config properties. This will allow the server to connect to the attacker's LDAP server and deserialize the LDAP response, which the attacker can use to execute java deserialization gadget chains on the Kafka connect server. Attacker can cause unrestricted deserialization of untrusted data (or) RCE vulnerability when there are gadgets in the classpath.

Since Apache Kafka 3.0.0, users are allowed to specify these properties in connector configurations for Kafka Connect clusters running with out-of-the-box configurations. Before Apache Kafka 3.0.0, users may not specify these properties unless the Kafka Connect cluster has been reconfigured with a connector client override policy that permits them.

Since Apache Kafka 3.9.1/4.0.0, we have added a system property ("-Dorg.apache.kafka.disallowed.login.modules") to disable the problematic login modules usage in SASL JAAS configuration. Also by default "com.sun.security.auth.module.JndiLoginModule,com.sun.security.auth.module.LdapLoginModule" are disabled in Apache Kafka Connect 3.9.1/4.0.0.

We advise the Kafka users to validate connector configurations and only allow trusted LDAP configurations. Also examine connector dependencies for vulnerable versions and either upgrade their connectors, upgrading that specific dependency, or removing the connectors as options for remediation. Finally, in addition to leveraging the "org.apache.kafka.disallowed.login.modules" system property, Kafka Connect users can also implement their own connector client config override policy, which can be used to control which Kafka client properties can be overridden directly in a connector config and which cannot.

When Connect workers in Apache Kafka 2.0.0, 2.0.1, 2.1.0, 2.1.1, 2.2.0, 2.2.1, or 2.3.0 are configured with one or more config providers, and a connector is created/updated on that Connect cluster to use an externalized secret variable in a substring of a connector configuration property value, then any client can issue a request to the same Connect cluster to obtain the connector's task configuration and the response will contain the plaintext secret rather than the externalized secrets variables.

A possible security vulnerability has been identified in Apache Kafka Connect API. This requires access to a Kafka Connect worker, and the ability to create/modify connectors on it with an arbitrary Kafka client SASL JAAS config and a SASL-based security protocol, which has been possible on Kafka Connect clusters since Apache Kafka Connect 2.3.0. When configuring the connector via the Kafka Connect REST API, an authenticated operator can set the sasl.jaas.config property for any of the connector's Kafka clients to "com.sun.security.auth.module.JndiLoginModule", which can be done via the producer.override.sasl.jaas.config, consumer.override.sasl.jaas.config, or admin.override.sasl.jaas.config properties. This will allow the server to connect to the attacker's LDAP server and deserialize the LDAP response, which the attacker can use to execute java deserialization gadget chains on the Kafka connect server. Attacker can cause unrestricted deserialization of untrusted data (or) RCE vulnerability when there are gadgets in the classpath.

Since Apache Kafka 3.0.0, users are allowed to specify these properties in connector configurations for Kafka Connect clusters running with out-of-the-box configurations. Before Apache Kafka 3.0.0, users may not specify these properties unless the Kafka Connect cluster has been reconfigured with a connector client override policy that permits them.

Since Apache Kafka 3.4.0, we have added a system property ("-Dorg.apache.kafka.disallowed.login.modules") to disable the problematic login modules usage in SASL JAAS configuration. Also by default "com.sun.security.auth.module.JndiLoginModule" is disabled in Apache Kafka Connect 3.4.0.

We advise the Kafka Connect users to validate connector configurations and only allow trusted JNDI configurations. Also examine connector dependencies for vulnerable versions and either upgrade their connectors, upgrading that specific dependency, or removing the connectors as options for remediation. Finally, in addition to leveraging the "org.apache.kafka.disallowed.login.modules" system property, Kafka Connect users can also implement their own connector client config override policy, which can be used to control which Kafka client properties can be overridden directly in a connector config and which cannot.