LangChain serialization injection vulnerability enables secret extraction

Description

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.

Recommendation

Update the langchain package to the latest compatible version. Followings are version details:

• Affected version(s): **< 0.3.37

  >= 1.0.0, < 1.2.3**

• Patched version(s): **0.3.37

  1.2.3**

References

• GHSA-r399-636x-v7f6
• CVE-2025-68665
• CWE-502
• CAPEC-310
• OWASP 2021-A6
• OWASP 2021-A8