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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.

PUBLISHED Reserved 2026-04-09 | Published 2026-04-10 | Updated 2026-04-13 | Assigner GitHub_M




MEDIUM: 5.6CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L

Problem types

CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')

Product status

< 0.5.18
affected

References

github.com/...th-sdk/security/advisories/GHSA-fw9q-39r9-c252

cve.org (CVE-2026-40190)

nvd.nist.gov (CVE-2026-40190)

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