CVE-2025-68665: Langchain Langchain.js

Critical severity, CVSS 9.1. EPSS: 0.8% chance of exploitation in the next 30 days.

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

Affected products

• Langchain Langchain.js: before 0.3.37 (fixed in 0.3.37); from 1.0.0, before 1.2.3 (fixed in 1.2.3)
• Langchain Langchain/core: before 0.3.80 (fixed in 0.3.80); from 1.0.0, before 1.1.8 (fixed in 1.1.8)

Published 2025-12-23. Last modified 2026-06-17.