fix: patch prototype pollution vulnerability in deepMix and mix

.gitignore

@@ -13,6 +13,7 @@ lerna-debug.log*
 # Node
 node_modules/
 yarn.lock
+package-lock.json
 
 # Build
 dist

__tests__/unit/lodash/deep-mix.spec.ts

@@ -0,0 +1,30 @@
+import deepMix from '../../../src/lodash/deep-mix';
+
+describe('deepMix', () => {
+  it('merges plain objects', () => {
+    const result = deepMix({}, { a: 1 }, { b: 2 });
+    expect(result).toEqual({ a: 1, b: 2 });
+  });
+
+  it('deep merges nested objects', () => {
+    const result = deepMix({ a: { x: 1 } }, { a: { y: 2 } });
+    expect(result).toEqual({ a: { x: 1, y: 2 } });
+  });
+
+  it('does not pollute Object.prototype via __proto__', () => {
+    const payload = JSON.parse('{"__proto__": {"polluted": true}}');
+    deepMix({}, payload);
+    expect((Object.prototype as any).polluted).toBeUndefined();
+  });
+
+  it('does not pollute via constructor.prototype', () => {
+    const payload = JSON.parse('{"constructor": {"prototype": {"polluted": true}}}');
+    deepMix({}, payload);
+    expect((Object.prototype as any).polluted).toBeUndefined();
+  });
+
+  it('does not pollute via prototype key', () => {
+    deepMix({}, { prototype: { polluted: true } });
+    expect((Object.prototype as any).polluted).toBeUndefined();
+  });
+});

__tests__/unit/lodash/mix.spec.ts

@@ -0,0 +1,25 @@
+import mix from '../../../src/lodash/mix';
+
+describe('mix', () => {
+  it('merges plain objects', () => {
+    const result = mix({} as any, { a: 1 }, { b: 2 });
+    expect(result).toEqual({ a: 1, b: 2 });
+  });
+
+  it('does not pollute Object.prototype via __proto__', () => {
+    const payload = JSON.parse('{"__proto__": {"polluted": true}}');
+    mix({}, payload);
+    expect((Object.prototype as any).polluted).toBeUndefined();
+  });
+
+  it('does not pollute via constructor key', () => {
+    const payload = JSON.parse('{"constructor": {"prototype": {"polluted": true}}}');
+    mix({}, payload);
+    expect((Object.prototype as any).polluted).toBeUndefined();
+  });
+
+  it('does not pollute via prototype key', () => {
+    mix({} as any, { prototype: { polluted: true } } as any);
+    expect((Object.prototype as any).polluted).toBeUndefined();
+  });
+});

src/lodash/deep-mix.ts

@@ -18,6 +18,10 @@ function _deepMix(dist, src, level?, maxLevel?) {
   maxLevel = maxLevel || MAX_MIX_LEVEL;
   for (const key in src) {
     if (hasOwn(src, key)) {
+      // Prevent prototype pollution by skipping dangerous keys
+      if (key === '__proto__' || key === 'constructor' || key === 'prototype') {
+        continue;
+      }
       const value = src[key];
       if (value !== null && isPlainObject(value)) {
         if (!isPlainObject(dist[key])) {

src/lodash/mix.ts

@@ -1,7 +1,15 @@
 // FIXME: Mutable param should be forbidden in static lang.
 function _mix<Base, Source>(dist: Base & Source, obj: Source): void {
   for (const key in obj) {
-    if (obj.hasOwnProperty(key) && key !== 'constructor' && obj[key] !== undefined) {
+    // Prevent prototype pollution by skipping dangerous keys
+    if (
+      key === '__proto__' ||
+      key === 'constructor' ||
+      key === 'prototype'
+    ) {
+      continue;
+    }
+    if (obj.hasOwnProperty(key) && obj[key] !== undefined) {
       (<any>dist)[key] = obj[key];
     }
   }