Run2 jackson security

Skill cxcscmu/SkillLearnBench/skills/b2-self-feedback-gemini-3.1-pro-preview/fix-security-bug/run2_jackson-security

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Security considerations for Jackson JSON deserialization in Java, focusing on @JacksonInject bypass vulnerabilities via empty property names ("").

SKILL.md

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Jackson Security: @JacksonInject Bypass Vulnerability

Concept

In Jackson, @JacksonInject is used to inject values into properties or constructor parameters during deserialization without expecting those values to come from the JSON payload itself. However, due to how Jackson's AnnotationIntrospector and fallback behaviors work, if a @JacksonInject annotated parameter does not explicitly have a @JsonProperty annotation, an attacker may be able to supply a JSON property with an empty string key ("") and bypass the injection mechanism.

This causes Jackson to deserialize the attacker's JSON value and bind it to the parameter instead of using the properly injected, trusted value.

Real-world Example (CVE-2021-25646 in Apache Druid)

Apache Druid used @JacksonInject for a JavaScriptConfig object in its JavaScriptDimFilter. By supplying "": {"enabled": true}, an attacker overrode the globally disabled JS config with an enabled one, allowing arbitrary code execution.

@JsonCreator
public JavaScriptDimFilter(
    @JsonProperty("dimension") String dimension,
    @JsonProperty("function") String function,
    // Vulnerable: no @JsonProperty, an empty string key "" will bind to this!
    @JacksonInject JavaScriptConfig config 
)

Mitigation

To mitigate this class of vulnerabilities at the framework level, you can implement a custom AnnotationIntrospector that refuses to parse empty string property names for parameters that don't explicitly specify one using @JsonProperty.

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.introspect.Annotated;
import com.fasterxml.jackson.databind.introspect.AnnotatedParameter;
import com.fasterxml.jackson.databind.introspect.NopAnnotationIntrospector;

public class SecureAnnotationIntrospector extends NopAnnotationIntrospector {
    @Override
    public JsonIgnoreProperties.Value findPropertyIgnorals(Annotated ac) {
        if (ac instanceof AnnotatedParameter) {
            final AnnotatedParameter ap = (AnnotatedParameter) ac;
            if (ap.hasAnnotation(JsonProperty.class)) {
                return JsonIgnoreProperties.Value.empty();
            }
        }
        // Deny empty string property names to prevent @JacksonInject bypasses
        return JsonIgnoreProperties.Value.forIgnoredProperties("");
    }
}