CVE-2026-40190
MEDIUMLangSmith Client SDKs has Prototype Pollution in langsmith-sdk via Incomplete `__proto__` Guard in Internal lodash `set()`
Title source: cnaDescription
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.
References (1)
Core 1
Core References
X_Refsource_Confirm x_refsource_confirm
https://github.com/langchain-ai/langsmith-sdk/security/advisories/GHSA-fw9q-39r9-c252
Scores
CVSS v3
5.6
EPSS
0.0023
EPSS Percentile
14.0%
Attack Vector
NETWORK
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
CISA SSVC
Vulnrichment
Exploitation
poc
Automatable
no
Technical Impact
partial
Details
CWE
CWE-1321
Status
published
Products (2)
langchain-ai/langsmith-sdk
< 0.5.18
npm/langsmith
0 - 0.5.18npm
Published
Apr 10, 2026
Tracked Since
Apr 11, 2026