GHSA-c4qx-w738-7hr3 - GraphQL Tools: Prototype pollution in mergeIncrementalResult via non-primitive path segments

## Report metadata | Field | Value | | --- | --- | | Package | `@graphql-tools/utils` (npm, `pkg:github/ardatan/graphql-tools`) | | Repository | https://github.com/ardatan/graphql-tools | | Component | `mergeIncrementalResult` / `setObjectKeyPath` (`packages/utils/src/mergeIncrementalResult.ts`) | | Vulnerability class | Prototype pollution (via unvalidated object path traversal) | | Verified against | Source read at `134d67ae36a559651f43ec7fe4a9da76f4a00c2b`; `master` HEAD `ccca0ff0dc8ea20726fd116b2f19a38709c30e62`; published npm builds 10.10.0, 10.10.1, 11.0.0, 12.0.0, 12.0.1 | | Affected versions | `@graphql-tools/utils` >= 10.10.1 through the scanned 12.0.0 source; introduced by `fbb58b51c4993ba9680ce6c2ef7203ab3a142713` ("remove dset dependency"). 12.0.1 also reproduces. 10.10.0 does not. | | API surface | Public, documented export (`packages/utils/src/index.ts:55`) | | Affected in default configuration | Yes — no options are involved; the forbidden-key check in `setObjectKeyPath` is the only defense and it is on by default | ## Summary `mergeIncrementalResult` merges an incremental GraphQL response part into an accumulated execution result by walking `['data', ...incrementalResult.path]` and assigning at the resolved location. `setObjectKeyPath` tries to reject dangerous segments with strict string equality against `'__proto__'`, `'constructor'` and `'prototype'` (lines 50-52 and 60-62), but it never validates that a path segment is a primitive string or number. A JSON path segment such as `["__proto__"]` is an array object, so `["__proto__"] !== '__proto__'` and the guard passes; the very next statement does `current[key]`, whose `ToPropertyKey` coercion turns that array into the string key `"__proto__"` and resolves `Object.prototype`. The following, innocuous-looking segment is then assigned directly onto `Object.prototype`. In a consuming app, `incrementalResult` is the response part being merged — data parsed from an upstream `@defer`/`@stream` multip