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CVE-2026-40190— LangSmith Client SDKs has Prototype Pollution in langsmith-sdk via Incomplete `__proto__` Guard in Internal lodash `set()`

Quick assessment

Affected
langchain-ai langsmith-sdk
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

LangSmith Client SDKs是LangChain开源的一个开发者工具包。 LangSmith Client SDKs 0.5.18之前版本存在安全漏洞，该漏洞源于LangSmith JavaScript/TypeScript SDK中内部提供的lodash set()工具的原型污染修复不完整，攻击者可能通过constructor.prototype污染Object.prototype。

CVSS 5.6 · Medium EPSS 0.39% · P30

Possible ATT&CK Techniques 1 AI

T1556 · Modify Authentication Process
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I. Basic Information for CVE-2026-40190

Vulnerability Information
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Vulnerability Title
LangSmith Client SDKs has Prototype Pollution in langsmith-sdk via Incomplete `__proto__` Guard in Internal lodash `set()`
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
CWE-1321
Source: CVE Program / CVE List V5
Vulnerability Title
LangSmith Client SDKs 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
LangSmith Client SDKs是LangChain开源的一个开发者工具包。 LangSmith Client SDKs 0.5.18之前版本存在安全漏洞，该漏洞源于LangSmith JavaScript/TypeScript SDK中内部提供的lodash set()工具的原型污染修复不完整，攻击者可能通过constructor.prototype污染Object.prototype。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
langchain-ai langsmith-sdk < 0.5.18 -

II. Public POCs for CVE-2026-40190

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III. Intelligence Information for CVE-2026-40190

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Vendor Advisories for CVE-2026-40190 (1)

IV. Related Vulnerabilities

Same product: langsmith-sdk
Same vendor: langchain-ai
Same weakness: CWE-1321

V. Comments for CVE-2026-40190

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