feat: block dangerous scope keys and harden findScope (#898)

Co-authored-by: Cursor <[email protected]>

test/integration/liquid/scope-security.spec.ts

@@ -0,0 +1,58 @@
+import { Liquid } from '../../../src/liquid'
+
+describe('scope security', function () {
+  let liquid: Liquid
+
+  beforeEach(function () {
+    liquid = new Liquid()
+  })
+
+  it('should not read __proto__ from passed scope', async function () {
+    const scope = JSON.parse('{"__proto__": {"polluted": true}, "name": "Alice"}')
+    await expect(liquid.parseAndRender('{{ name }}', scope)).resolves.toBe('Alice')
+    await expect(liquid.parseAndRender('{{ __proto__.polluted }}', scope)).resolves.toBe('')
+  })
+
+  it('should not read constructor from passed scope', async function () {
+    const scope = { name: 'Alice', constructor: { name: 'Object' } }
+    await expect(liquid.parseAndRender('{{ constructor.name }}', scope)).resolves.toBe('')
+  })
+
+  it('should not read prototype chain properties by default', async function () {
+    const scope = { user: Object.create({ isAdmin: true, name: 'Inherited' }) }
+    scope.user.name = 'Alice'
+    await expect(liquid.parseAndRender('{{ user.name }}', scope)).resolves.toBe('Alice')
+    await expect(liquid.parseAndRender('{{ user.isAdmin }}', scope)).resolves.toBe('')
+  })
+
+  it('should not expose Object.prototype keys from polluted scope', async function () {
+    const scope = Object.create({ polluted: 'yes' })
+    scope.safe = 'ok'
+    await expect(liquid.parseAndRender('{{ safe }}', scope)).resolves.toBe('ok')
+    await expect(liquid.parseAndRender('{{ polluted }}', scope)).resolves.toBe('')
+  })
+
+  it('should block assign to __proto__ from being read back', async function () {
+    await expect(liquid.parseAndRender(
+      '{% assign __proto__ = obj %}{{ __proto__.polluted }}',
+      { obj: { polluted: true } }
+    )).resolves.toBe('')
+  })
+
+  it('should still allow increment on user scope', async function () {
+    const scope = { counter: 0 }
+    await expect(liquid.parseAndRender('{% increment counter %}', scope)).resolves.toBe('0')
+    await expect(liquid.parseAndRender('{% increment counter %}', scope)).resolves.toBe('1')
+    expect(scope.counter).toBe(2)
+  })
+
+  it('should allow ownPropertyOnly=false to read prototype values', async function () {
+    const scope = { foo: Object.create({ bar: 'BAR' }) }
+    await expect(liquid.parseAndRender('{{ foo.bar }}', scope, { ownPropertyOnly: false })).resolves.toBe('BAR')
+  })
+
+  it('should still block __proto__ when ownPropertyOnly=false', async function () {
+    const scope = { foo: { __proto__: { bar: 'BAR' } } }
+    await expect(liquid.parseAndRender('{{ foo.__proto__.bar }}', scope, { ownPropertyOnly: false })).resolves.toBe('')
+  })
+})