CVE-2026-40190: LangSmith Client SDKs provide SDK's for interacting with the LangSmith platform

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MEDIUM 5.6REMOTEUPGRADE

CVE-2026-40190 is a medium-severity flaw (CVSS 5.6) affecting langsmith. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 createAno

Why this priority

Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.6 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 76%)
CISA exploited list	No
Weakness	CWE-1321
Published	2026-04-10
Last modified	2026-10-26

Publisher (CNA): GitHub, Inc. · Vendor: langchain

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-10 20:16 UTCPublished CVE record published
2026-10-26 21:10 UTCUpdated Record last modified

langchain langsmith UPGRADE

Affected: < 0.5.18

Fixed in: 0.5.18

Safe to downgrade to: no unaffected older release

1. Check installed version

npm ls langsmith

2. UPGRADE to 0.5.18

npm install langsmith@">=0.5.18"

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-40190?

langsmith: upgrade to 0.5.18. Exact commands for each OS are on this page.

Is CVE-2026-40190 being exploited?

CVE-2026-40190 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-40190 affect?

CVE-2026-40190 affects langsmith. Severity is medium (CVSS 5.6). 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() uti

How urgent is CVE-2026-40190?

Priority 36/100. Public exploit reference; Remotely exploitable, no login, no user action

Software pages

OpenAI and LLM tools vulnerabilities · Lodash vulnerabilities

References

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