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TI-2026-29004 Aliases CVE-2026-40190GHSA-fw9q-39r9-c252

Prototype pollution in langchain-ai langsmith-sdk

Priority HIGH 75CWE-1321Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
—
Confidentiality · integrity · availability
High · High · High
Fix status
Fixed

Attack profile from CVSS 3.1 · NVD. Fix status from CNA and GitHub.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00325 25th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Fixed langsmith-sdk (langchain-ai): 0.5.18langsmith (npm): 0.5.18

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
langchain-ailangsmith-sdkbefore 0.5.180.5.18Patch availableCNA
—langsmith (npm)before 0.5.180.5.18Patch availableGHSA-fw9q-39r9-c252
  • langsmith-sdk Vendorlangchain-ai Affected before 0.5.18 Fixed in 0.5.18 Patch available CNA
  • langsmith (npm) Vendor— Affected before 0.5.18 Fixed in 0.5.18 Patch available GHSA-fw9q-39r9-c252

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:langchain:langsmith:*:*:*:*:*:node.js:*:*before 0.5.18Vulnerablelangchain-ai
  • cpe:2.3:a:langchain:langsmith:*:*:*:*:*:node.js:*:* Versions before 0.5.18 Vulnerable ·langchain-ai

Remediation

  • Fix · CNA langsmith-sdk (langchain-ai) Fixed in 0.5.18
  • Fix · GHSA-fw9q-39r9-c252 langsmith (npm) Fixed in 0.5.18 Advisory →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-40190
  2. 2026-10-03 Alias added: GHSA-fw9q-39r9-c252

References

Exploit 1

Advisory 1

Other 3

  • TI-2026-20818 LangSmith Studio has URL Parameter Injection Vulnerability that Enables Token Theft via Malicious baseUrl CVSS 4.0HIGH 8.5

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences