CVE-2026-40190CWE-1321

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

Medium · published April 10, 2026

CVSS v3.1
5.6
EPSS
0%
Percentile
31.4
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
5.6 · MEDIUM
Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
CVSS v4.0
Not supplied
EPSS
0.00385 · 31.4th percentile
Weakness
CWE-1321 · Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
Published
2026-04-10T19:47Z
EPSS history
Timeline
  • 10 APR 19:47Z
    LangSmith Client SDKs has Prototype Pollution in langsmith-sdk via Incomplete `__proto__` Guard in Internal lodash `set()`
    cvelistv5