CVE-2026-40190
The baseAssignValue() function only guards against the __proto__ key, but fails to prevent traversal via constructor.prototype.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.31%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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.
- CVSS 3.1
- 9.8 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- EPSS
- 0.31% probability · 24th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-1321
- Affected
- langchain/langsmith
- Source
- security-advisories@github.com
References
- https://github.com/langchain-ai/langsmith-sdk/security/advisories/GHSA-fw9q-39r9-c252Exploit, Vendor Advisory, Mitigation
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.