Description
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; langchain: langchain\/core
References5
- github.com/langchain-ai/langchainjs/security/advisories/GHSA-r3… Vendor Advisory
- github.com/langchain-ai/langchainjs/security/advisories/GHSA-r3… Vendor Advisory
- github.com/langchain-ai/langchainjs/commit/e5063f9c6e9989ea067d… Patch
- github.com/langchain-ai/langchainjs/releases/tag/%40langchain%2… Release Notes
- github.com/langchain-ai/langchainjs/releases/tag/langchain%401.… Release Notes
Metrics
- CVSS 3.1
-
9.1
CRITICAL
Score source: NVD
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N - EPSS — exploit probability
- 1% percentile: 57 · as of 11 November 2026
- CWE
- CWE-502
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.