---
id: CVE-2026-40190
title: >-
  LangSmith Client SDKs provide SDK's for interacting with the LangSmith
  platform
summary: >-
  LangSmith Client SDKs provide SDK's for interacting with the LangSmith
  platform. Prior to 0.5.18, the LangSmith JavaScript/TypeScript SDK (langsmith)
  contains an incomplete prototype pollution fix in its internally vendored
  lodash set() …
severity: medium
cvss: 5.6
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L'
cwe:
  - CWE-1321
vendor: langchain
product: langsmith
affected:
  - langsmith < 0.5.18
patched:
  - langsmith 0.5.18
published: '2026-04-10'
updated: '2026-07-07'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-40190'
references:
  - url: >-
      https://github.com/langchain-ai/langsmith-sdk/security/advisories/GHSA-fw9q-39r9-c252
    label: security-advisories@github.com
tags:
  - nvd
epss: 0.00313
epssPercentile: 0.24479
ingestedAt: '2026-07-07T18:42:24.204Z'
---

## Overview

LangSmith Client SDKs provide SDK's for interacting with the LangSmith platform. Prior to 0.5.18, the LangSmith JavaScript/TypeScript SDK (langsmith) contains an incomplete prototype pollution fix in its internally vendored lodash set() utility. The baseAssignValue() function only guards against the __proto__ key, but fails to prevent traversal via constructor.prototype. This allows an attacker who controls keys in data processed by the createAnonymizer() API to pollute Object.prototype, affecting all objects in the Node.js process. This vulnerability is fixed in 0.5.18.

## Affected

- `langsmith < 0.5.18`

## Remediation

Upgrade past the affected range:

- `langsmith 0.5.18`