What’s Vulnerable › Vulnerabilities
CVE-2026-40190: LangSmith Client SDKs has Prototype Pollution in langsmith-sdk via Incomplete `__proto__` Guard in Internal lodash `set()`
- Severity: critical (CVSS 9.8 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.3% probability of exploitation in the next 30 days
- Public exploit or detection template: yes
- Published: 2026-04-10 · updated 2026-10-26
- Weakness: 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 products
- langchain-ai langsmith-sdk: before 0.5.18 — fixed in 0.5.18
How to fix
Upgrade to a fixed version: langchain-ai langsmith-sdk 0.5.18. Check the vendor advisory for mitigations.
References
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