druid-jackson-security

name	druid-jackson-security
description	Securing Apache Druid's JavaScriptConfig deserialization. Use this skill whenever patching or securing Jackson deserialization in Druid, especially regarding the empty key ("") bypass.

Druid Jackson Deserialization Security

The Vulnerability

In Apache Druid 0.20.0, a vulnerability exists where authenticated attackers can execute arbitrary code by passing malicious JavaScript payloads. The vulnerability exploits a known Jackson deserialization behavior: when a class constructor uses @JacksonInject without specifying a property name or disabling user input, Jackson defaults the property name to "" (empty string).

Attackers can provide an empty key ("") in the JSON payload to override the safely injected JavaScriptConfig instance with a malicious one where enabled is set to true. This bypasses Druid's internal check that disables JavaScript by default.

Example Payload Fragment:

{
  "type": "javascript",
  "function": "function(){java.lang.Runtime.getRuntime().exec('malicious_command');}",
  "": {
    "enabled": true
  }
}

The Fix

To remediate this vulnerability, we must prevent JSON input from overriding the injected JavaScriptConfig. Jackson provides the OptBoolean.FALSE value for the useInput attribute of the @JacksonInject annotation precisely for this purpose.

For every occurrence of @JacksonInject JavaScriptConfig inside a @JsonCreator constructor, modify the annotation to explicitly reject input data:

import com.fasterxml.jackson.annotation.OptBoolean;

// ...

@JsonCreator
public MyJavaScriptComponent(
    // ...
    @JacksonInject(useInput = OptBoolean.FALSE) JavaScriptConfig config
)

By adding useInput = OptBoolean.FALSE, Jackson will ignore any JSON property (including "") that attempts to bind to the config parameter, and will exclusively use the JavaScriptConfig instance provided by the Guice injector.

Affected Classes

You should locate and patch the following classes that inject JavaScriptConfig:

1. JavaScriptWorkerSelectStrategy.java
2. JavaScriptPostAggregator.java
3. JavaScriptAggregatorFactory.java
4. JavaScriptExtractionFn.java
5. JavaScriptDimFilter.java
6. JavaScriptParseSpec.java
7. JavaScriptTieredBrokerSelectorStrategy.java