CVE-2023-34040: Spring for Apache Kafka Deserialization Vulnerability and Mitigation

A recently discovered vulnerability (CVE-2023-34040) in Spring for Apache Kafka versions 3..9 and earlier, as well as versions 2.9.10 and earlier, has been found to potentially allow deserialization attacks when specific, unusual configurations are applied. This blog post will discuss the conditions under which the vulnerability can be exploited, provide code snippets to demonstrate the issue, link to original references, and provide details on how to mitigate the risk associated with this CVE.

Description and Exploit

To exploit this vulnerability, an attacker must first construct a malicious serialized object in one of the deserialization exception record headers. Applications that are vulnerable must meet all three of the following conditions:

1. The user does not configure an ErrorHandlingDeserializer for the key and/or value of the record.
2. The user explicitly sets container properties checkDeserExWhenKeyNull and/or checkDeserExWhenValueNull container properties to true.

The user allows untrusted sources to publish to a Kafka topic.

By default, the properties checkDeserExWhenKeyNull and checkDeserExWhenValueNull are set to false. The container would only attempt to deserialize the headers if an ErrorHandlingDeserializer is configured. If properly set up, the ErrorHandlingDeserializer prevents the vulnerability by removing any malicious headers before processing the record.

Here is a sample configuration in which the vulnerability is present

@Autowired
public void configureKafkaListenerContainerFactory(KafkaListenerContainerFactory<?> factory) {
    factory.setCheckDeserExWhenKeyNull(true);
    factory.setCheckDeserExWhenValueNull(true);
}

In order to mitigate this vulnerability, one should configure the ErrorHandlingDeserializer as follows:

@Bean
public Map<String, Object> consumerConfigs() {
    Map<String, Object> props = new HashMap<>();
    ...
    props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, ErrorHandlingDeserializer.class);
    props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, ErrorHandlingDeserializer.class);
    ...
    return props;
}

For further information, you can consult the following sources

1. CVE-2023-34040 in the National Vulnerability Database
2. Spring for Apache Kafka Reference Documentation (3..9)
3. ErrorHandlingDeserializer JavaDoc

Mitigation

In order to protect your application from this vulnerability, ensure that you configure an ErrorHandlingDeserializer for both key and value deserialization. Additionally, make sure to not explicitly set the container properties checkDeserExWhenKeyNull and checkDeserExWhenValueNull to true. Finally, it is always recommended to not allow untrusted sources to publish to your Kafka topics.

Conclusion

While this CVE-2023-34040 vulnerability only affects applications with very specific configurations, it is essential to take all necessary steps to protect your application from possible exploitation. By setting up an ErrorHandlingDeserializer and following the best practices recommended in the original references, you can mitigate the risks associated with this found issue in Spring for Apache Kafka.

Timeline

Published on: 08/24/2023 13:15:00 UTC
Last modified on: 08/29/2023 15:58:00 UTC