scim-patch: Mutation of Inherited Built-in Method Objects

## Summary Incomplete Prototype Pollution Fix Allows Mutation of Inherited Built-in Method Objects `scim-patch` blocks direct dangerous path segments such as `__proto__`, `constructor`, and `prototype`, but still traverses inherited properties when applying SCIM patch paths. An attacker who controls a SCIM PATCH operation can use paths such as `toString.polluted` to mutate shared built-in function objects, for example `Object.prototype.toString`. ## Impact A malicious patch can add attacker-controlled properties to inherited built-in method objects. The impact is narrower than direct `Object.prototype` pollution, but the mutation is process-global and may affect application logic that reads properties from inherited methods. ## Details Affected code paths: - `navigate()` reads inherited properties via `schema[subPath]` - `assign()` uses `key in obj`, which treats inherited properties as existing Because inherited keys are followed, safe-looking path segments such as `toString` can resolve to shared built-in objects. ## PoC ```js const assert = require("node:assert/strict"); const { scimPatch } = require("./lib/src/scimPatch"); const victim = { schemas: ["urn:ietf:params:scim:schemas:core:2.0:User"], userName: "alice", active: true, emails: [{ value: "alice@example.com", primary: true }], meta: { created: "x", lastModified: "x", resourceType: "User" } }; try { assert.equal(({}).toString.scimPatchPolluted, undefined); scimPatch(victim, [ { op: "add", path: "toString.scimPatchPo