CVE-2025-68665

LangChain is a framework for building LLM-powered applications. Prior to @langchain/core versions 0.3.80 and 1.1.8, and prior to langchain versions 0.3.37 and 1.2.3, a serialization injection vulnerability exists in LangChain JS's toJSON() method (and subsequently when string-ifying objects using JSON.stringify(). The method did not escape objects with 'lc' keys when serializing free-form data in kwargs. The 'lc' key is used internally by LangChain to mark serialized objects. When user-controlled data contains this key structure, it is treated as a legitimate LangChain object during deserialization rather than plain user data. This issue has been patched in @langchain/core versions 0.3.80 and 1.1.8, and langchain versions 0.3.37 and 1.2.3

An adversary targeting a LangChain JS-powered chatbot or API crafts a JSON payload containing a nested object with the 'lc' key structure used internally by LangChain (e.g., {"input": {"lc": 1, "type": "constructor", "id": ["langchain", "...TargetClass"], "kwargs": {...}}}). When this user-controlled data flows into LangChain's toJSON() or is passed through JSON.stringify(), the framework treats it as a legitimate serialized LangChain object rather than plain user data. During subsequent deserialization, LangChain instantiates the attacker-specified class with attacker-controlled kwargs. Depending on available gadget classes in the runtime context, this can achieve arbitrary file reads, environment variable exfiltration, or code execution — all via a single crafted HTTP request to a public API endpoint.