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LangsmithApplication · Langchain

CVE-2026-40190

CRITICAL · 9.8 CVSS v3.1 Published 2026-04-10
Fix available
A fix is available. Upgrade to 0.5.18 or later.
See remediation →
100/100
Remediation priority · Urgent
Public exploit Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

The LangSmith JavaScript/TypeScript SDK contains an incomplete prototype pollution fix in its vendored lodash set() utility. The baseAssignValue() function guards against direct __proto__ key assignment but fails to prevent traversal via constructor.prototype, allowing attackers who control keys in data processed by the createAnonymizer() API to pollute Object.prototype and affect all objects in the Node.js process.

MitigationUpgrade the langsmith SDK to version 0.5.18 or later to apply the complete prototype pollution fix.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
LangsmithApplication
Affected:< 0.5.18

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed langsmith SDK version
    Run 'npm list langsmith' or check package.json for the langsmith dependency version entry
    Affected if The version listed is lower than 0.5.18 (e.g., 0.5.17, 0.5.0, etc.)
  2. Check for createAnonymizer usage in codebase
    Search your codebase for imports or usage of 'createAnonymizer' from langsmith (e.g., grep for 'createAnonymizer' or 'from "langsmith"')
    Affected if The createAnonymizer function is imported and used in your application code
  3. Inspect anonymizer input data flow
    Review where createAnonymizer is called and examine whether external/user-controlled data can reach the 'keys' parameter passed to this function
    Affected if Untrusted input can influence the keys argument passed to createAnonymizer, enabling prototype pollution via constructor.prototype traversal
  4. Verify lodash set() protection in langsmith
    If possible, inspect the bundled langsmith node_modules/langsmith/dist/cjs/utils.js (or similar) and locate the baseAssignValue function to confirm it only checks __proto__ and not constructor.prototype
    Affected if The baseAssignValue function lacks protection against constructor.prototype key traversal
  5. Confirm Node.js runtime context
    Verify this runs in a Node.js environment (not browser) as prototype pollution via constructor.prototype is a Node.js-specific attack vector for this flaw
    Affected if Your application runs in Node.js and uses the vulnerable langsmith SDK version

You are affected if your installed langsmith SDK version is below 0.5.18 AND your code uses createAnonymizer with potentially untrusted input in the keys parameter.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 0.5.18 or later
Fixed in 0.5.18
Interim mitigation

Upgrade the langsmith SDK to version 0.5.18 or later to apply the complete prototype pollution fix.

Recommended fix High confidence

0.5.18 or later

  1. Identify all projects and dependencies that include the langsmith package
  2. Update the langsmith package to version 0.5.18 or later using your package manager (e.g., npm install [email protected] or npm update langsmith)
  3. Verify the installed version is 0.5.18 or higher by checking package.json or running npm list langsmith
  4. Test the application to ensure the update does not break existing functionality, particularly any usage of createAnonymizer() API

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Langsmith Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing3.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,210
Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-40190 in production — separate from our analysis above.

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What this is

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What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data