Paper/Archive/CVE-2026-40190

CVE-2026-40190

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

EPSS 0.3%public exploit CVSS 9.8

critical.is priorityof 100

CVSS 9.8 (NVD)9.8 / 10 × 3029.4 Not in CISA KEV+300.0 EPSS percentile 24.2.242 × 204.8 Exploit: SSVC poc+1010.0 SSVC exploitation: poc+100.0

Description · from the CVE record

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

ProductAffectedFixed inSource

langsmith-sdk< 0.5.18–CNA

Scores by source

NVD9.8CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

GitHub_M (CNA)5.6CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L

CISA ADPSSVCExploitation: poc · Automatable: no · Technical impact: partial

References

refgithub.com/langchain-ai/langsmith-sdk/security/advisories/GHSA-fw9q-39r9-c252