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

> CVE-2026-40190: LangSmith Client SDKs has Prototype Pollution in langsmith-sdk via Incomplete `__proto__` Guard in Internal lodash `set()`. CVSS 5.6 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-40190
Last updated: 2026-07-07T18:33:24Z

- Published: 2026-04-10 19:47 UTC · Updated: 2026-07-07 18:33 UTC · Assigner: GitHub\_M
- CVSS: 5.6 (CVSS 3.1) · Severity: Medium · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
- EPSS: 0.31%, 24th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-1321

## 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.

## Affected vendors and products

- langchain-ai: langsmith-sdk

## Tracked companies

- [LangChain (LangSmith)](https://rewindex.com/company/langchain-langsmith.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-40190)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-40190)
- [https://github.com/langchain-ai/langsmith-sdk/security/advisories/GHSA-fw9q-39r9-c252](https://github.com/langchain-ai/langsmith-sdk/security/advisories/GHSA-fw9q-39r9-c252)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-40190 · Markdown: https://rewindex.com/cve/CVE-2026-40190.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-40190 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T02:14:26.291Z