Disable JavaScript Execution in Druid Filters

Disabling JavaScript Filter Execution

Problem

Even if empty key validation is in place, the "type": "javascript" filter capability itself is a code execution vector. The security sandbox can be disabled or bypassed.

Solution: Disable JavaScript Filters at Configuration Level

Implementation Strategy

1. Identify JavaScript Filter Registration

   • Find JavaScriptDimFilter class and its factory registration
   • Locate where filter types are registered (likely in a filter registry or module)
   • Find where JavaScript evaluation is initialized

2. Create Security Configuration

   • Add a Druid configuration property to disable JavaScript filters
   • Default to disabled (secure-by-default)
   • Prevent re-enabling via ObjectMapper annotations or runtime configuration

3. Enforcement Approach

   Option A: Remove from Filter Registry

   • Unregister JavaScriptDimFilter from the factory
   • During module initialization, skip registration of JavaScript filter type
   • Returns 400 Bad Request if client attempts to use it

   Option B: Reject at Deserialization

   • Create a custom deserializer for filter JSON
   • If type == "javascript", throw JsonMappingException immediately
   • Prevents any JavaScript filter from being instantiated

4. Configuration Property

   druid.javascript.enabled=false  (default, required for security)
   

Code Pattern

// In filter factory or deserializer
if ("javascript".equals(filterType)) {
    if (!isJavaScriptEnabled()) {
        throw new IllegalArgumentException(
            "JavaScript filters are disabled. " +
            "Set druid.javascript.enabled=true to enable (not recommended)."
        );
    }
}

private static boolean isJavaScriptEnabled() {
    // Check configuration, default false
    return config.getBoolean("druid.javascript.enabled", false);
}

Defense in Depth

• Even if an attacker bypasses empty key validation, they cannot execute JavaScript
• JavaScript evaluation engine should not be initialized if disabled
• Configuration should be immutable once the server starts