run2_jackson-inject-security

Jackson @JacksonInject Security: Preventing Input Override

Vulnerability

Jackson's @JacksonInject allows server-injected values to be overridden by JSON input. An attacker can use an empty key "" in the JSON payload to inject a custom object that replaces the server-configured value.

How the Empty Key Attack Works

When Jackson deserializes a class with @JacksonInject:

1. It first sets the injected value from InjectableValues
2. Then it processes JSON properties, including empty-string keys ""
3. The empty key "" can match the injectable parameter, overriding the server value

Example Attack Payload

{
  "type": "javascript",
  "dimension": "dim",
  "function": "function(x){java.lang.Runtime.getRuntime().exec('cmd')}",
  "": {"enabled": true}
}

Fix: Use OptBoolean.FALSE

Code Change

// BEFORE (vulnerable):
import com.fasterxml.jackson.annotation.JacksonInject;

@JsonCreator
public MyClass(@JacksonInject MyConfig config) { ... }

// AFTER (secure):
import com.fasterxml.jackson.annotation.JacksonInject;
import com.fasterxml.jackson.annotation.OptBoolean;

@JsonCreator
public MyClass(@JacksonInject(useInput = OptBoolean.FALSE) MyConfig config) { ... }

What useInput = OptBoolean.FALSE Does

• Tells Jackson to NEVER use JSON input for this parameter
• Only the server-injected value from InjectableValues is used
• Any JSON property (including empty key "") attempting to set this parameter is ignored

Compatibility

• Requires Jackson 2.9+ (available in Jackson 2.10.2 used by Druid 0.20.0)
• com.fasterxml.jackson.annotation.OptBoolean import required

Patch Generation Workflow

# 1. Make changes to source files
# 2. Generate unified diff patch
cd /root/druid && git diff > /root/patches/fix.patch

# 3. To apply on clean repo:
cd /root/druid && git apply /root/patches/fix.patch

# 4. Build specific module with all dependencies:
mvn clean package -DskipTests -Dcheckstyle.skip=true -Dpmd.skip=true \
  -Dforbiddenapis.skip=true -Dspotbugs.skip=true -Danimal.sniffer.skip=true \
  -Denforcer.skip=true -Djacoco.skip=true -Ddependency-check.skip=true \
  -pl '!web-console' -pl indexing-service -am