Prototype Pollution in JavaScript Runtimes: Exploitation Mechanics, Runtime Propagation, and Secure Mitigation Strategies

This work presents a rigorous technical investigation of prototype pollution as a structural vulnerability in modern JavaScript runtimes, with particular emphasis on Node.js execution environments and server-side object lifecycle manipulation. Unlike conventional injection classes that target isolated execution paths, prototype pollution compromises the semantic foundation of object inheritance, enabling adversarial influence over application logic at runtime scale. The study examines how unsafe recursive merge operations, configuration hydration patterns, and deserialization of untrusted JSON inputs can lead to unauthorized modification of Object.prototype, thereby altering the behavioral properties of all subsequently instantiated objects. Through a controlled experimental environment, this research demonstrates how adversarial payloads leveraging constructor.prototype and related inheritance entry points propagate across runtime contexts, producing systemic effects such as authorization bypass, policy corruption, and cross-component trust failures. The methodological framework combines: formal analysis of JavaScript’s prototype-based inheritance model, runtime instrumentation and behavioral validation in Node.js, adversarial payload construction and propagation tracing, secure refactoring strategies based on object isolation and input constraint models. The experimental results show that prototype pollution is best understood not as a traditional input validation failure, but as a meta-layer vulnerability capable of altering the ontological assumptions of object identity and trust boundaries within dynamic language ecosystems. By modifying prototype chains, attackers do not merely inject data; they reshape the interpretive context in which application logic executes. From a defensive standpoint, the work proposes a security engineering model grounded in: explicit exclusion of structural inheritance keys (__proto__, constructor, prototype), adoption of null-prototype object construction (Object.create(null)), schema-enforced input validation pipelines, and architectural constraints that prevent implicit trust propagation through inheritance. This research situates prototype pollution within a broader class of semantic integrity violations analogous to type confusion and class hierarchy poisoning observed in lower-level languages, highlighting its role as a foundational enabler for higher-order exploitation chains, including authentication bypass, configuration poisoning, and indirect remote code execution vectors. The contribution is both practical and theoretical: it provides a reproducible laboratory, complete exploitation workflow, and engineering mitigation framework, while also framing prototype pollution as a systemic risk emerging from the intersection of dynamic language semantics, supply chain dependency models, and modern server-side JavaScript architectures. The findings are intended to support advanced security research, secure software engineering practices, and the development of hardened runtime environments capable of preserving prototype integrity under adversarial conditions.