diff --git a/src/helpers.js b/src/helpers.js
index 3eec10db..66b649c2 100644
--- a/src/helpers.js
+++ b/src/helpers.js
@@ -193,6 +193,21 @@ export default function Helpers(mpInstance) {
             if ((options = arguments[i]) != null) {
                 // Extend the base object
                 for (name in options) {
+                    // Prevent prototype pollution
+                    // https://github.com/advisories/GHSA-jf85-cpcp-j695
+                    if (
+                        name === '__proto__' ||
+                        name === 'constructor' ||
+                        name === 'prototype'
+                    ) {
+                        continue;
+                    }
+
+                    // Only copy own properties
+                    if (!Object.prototype.hasOwnProperty.call(options, name)) {
+                        continue;
+                    }
+
                     src = target[name];
                     copy = options[name];
 
diff --git a/test/jest/helpers-prototype-pollution.spec.ts b/test/jest/helpers-prototype-pollution.spec.ts
new file mode 100644
index 00000000..51d410e9
--- /dev/null
+++ b/test/jest/helpers-prototype-pollution.spec.ts
@@ -0,0 +1,256 @@
+import Helpers from '../../src/helpers';
+
+describe('Helpers - Prototype Pollution Protection', () => {
+    let helpers: any;
+    let mockMpInstance: any;
+
+    beforeEach(() => {
+        // Clear any potential pollution
+        delete (Object.prototype as any).isAdmin;
+        delete (Object.prototype as any).polluted;
+        delete (Object.prototype as any).testProp;
+
+        mockMpInstance = {
+            _Store: {
+                SDKConfig: {
+                    flags: {}
+                }
+            },
+            Logger: {
+                verbose: jest.fn(),
+                warning: jest.fn(),
+                error: jest.fn()
+            }
+        };
+
+        helpers = new Helpers(mockMpInstance);
+    });
+
+    afterEach(() => {
+        // Cleanup
+        delete (Object.prototype as any).isAdmin;
+        delete (Object.prototype as any).polluted;
+        delete (Object.prototype as any).testProp;
+    });
+
+    describe('extend() - Prototype Pollution Prevention', () => {
+        it('should block __proto__ in shallow merge', () => {
+            const malicious = JSON.parse('{"__proto__": {"isAdmin": true}}');
+            const result = helpers.extend({}, malicious);
+
+            expect(typeof result).toBe('object');
+            const testObj = {};
+            expect((testObj as any).isAdmin).toBeUndefined();
+            expect((Object.prototype as any).isAdmin).toBeUndefined();
+        });
+
+        it('should block __proto__ in deep merge', () => {
+            const malicious = JSON.parse('{"__proto__": {"polluted": "yes"}}');
+            const result = helpers.extend(true, {}, malicious);
+
+            expect(typeof result).toBe('object');
+            const testObj = {};
+            expect((testObj as any).polluted).toBeUndefined();
+            expect((Object.prototype as any).polluted).toBeUndefined();
+        });
+
+        it('should block constructor property', () => {
+            const malicious = JSON.parse('{"constructor": {"polluted": "constructor"}}');
+            const result = helpers.extend({}, malicious);
+
+            expect(typeof result).toBe('object');
+            const testObj = {};
+            expect((testObj as any).polluted).toBeUndefined();
+        });
+
+        it('should block prototype property', () => {
+            const malicious = JSON.parse('{"prototype": {"polluted": "prototype"}}');
+            const result = helpers.extend({}, malicious);
+
+            expect(typeof result).toBe('object');
+            const testObj = {};
+            expect((testObj as any).polluted).toBeUndefined();
+        });
+
+        it('should only copy own properties', () => {
+            const parent = { inherited: 'value' };
+            const child = Object.create(parent);
+            child.own = 'ownValue';
+
+            const result = helpers.extend({}, child);
+
+            expect(result.own).toBe('ownValue');
+            expect(result.inherited).toBeUndefined();
+        });
+
+        it('should still merge normal properties correctly', () => {
+            const source = {
+                name: 'John',
+                age: 30,
+                address: {
+                    city: 'NYC',
+                    zip: '10001'
+                }
+            };
+
+            const result = helpers.extend(true, {}, source);
+
+            expect(result.name).toBe('John');
+            expect(result.age).toBe(30);
+            expect(result.address.city).toBe('NYC');
+            expect(result.address.zip).toBe('10001');
+        });
+
+        it('should handle nested objects without pollution', () => {
+            const malicious = {
+                user: {
+                    name: 'John',
+                    __proto__: { isAdmin: true }
+                }
+            };
+
+            const result = helpers.extend(true, {}, malicious);
+
+            expect(result.user.name).toBe('John');
+            
+            const testObj = {};
+            expect((testObj as any).isAdmin).toBeUndefined();
+            expect((Object.prototype as any).isAdmin).toBeUndefined();
+        });
+
+        it('should handle multiple source objects', () => {
+            const obj1 = { a: 1 };
+            const obj2 = { b: 2 };
+            const malicious = JSON.parse('{"__proto__": {"polluted": true}}');
+
+            const result = helpers.extend({}, obj1, obj2, malicious);
+
+            expect(result.a).toBe(1);
+            expect(result.b).toBe(2);
+
+            const testObj = {};
+            expect((testObj as any).polluted).toBeUndefined();
+        });
+
+        it('should handle arrays correctly', () => {
+            const source = {
+                items: [1, 2, 3],
+                nested: {
+                    arr: ['a', 'b']
+                }
+            };
+
+            const result = helpers.extend(true, {}, source);
+
+            expect(Array.isArray(result.items)).toBe(true);
+            expect(result.items).toEqual([1, 2, 3]);
+            expect(result.nested.arr).toEqual(['a', 'b']);
+        });
+
+        it('should handle objects with null prototype (Object.create(null))', () => {
+            const nullProtoObj = Object.create(null);
+            nullProtoObj.name = 'test';
+            nullProtoObj.value = 42;
+
+            const result = helpers.extend({}, nullProtoObj);
+
+            expect(result.name).toBe('test');
+            expect(result.value).toBe(42);
+        });
+
+        it('should handle objects with null prototype in deep merge', () => {
+            const nullProtoObj = Object.create(null);
+            nullProtoObj.nested = Object.create(null);
+            nullProtoObj.nested.deep = 'value';
+
+            const result = helpers.extend(true, {}, nullProtoObj);
+
+            expect(result.nested.deep).toBe('value');
+        });
+
+        it('should handle null/undefined source arguments gracefully', () => {
+            const obj1 = { a: 1 };
+            const obj2 = { b: 2 };
+
+            const result = helpers.extend({}, obj1, null, obj2, undefined);
+
+            expect(result.a).toBe(1);
+            expect(result.b).toBe(2);
+        });
+
+        it('should handle null/undefined source arguments in deep merge', () => {
+            const obj1 = { a: { nested: 1 } };
+            const obj2 = { b: { nested: 2 } };
+
+            const result = helpers.extend(true, {}, obj1, null, obj2, undefined);
+
+            expect(result.a.nested).toBe(1);
+            expect(result.b.nested).toBe(2);
+        });
+
+        it('should handle all null/undefined sources', () => {
+            const target = { existing: 'value' };
+
+            const result = helpers.extend(target, null, undefined, null);
+
+            expect(result.existing).toBe('value');
+            expect(result).toBe(target);
+        });
+    });
+
+    describe('Real-world attack scenarios', () => {
+        it('should protect against localStorage-based attack', () => {
+            // Simulate malicious localStorage data
+            const localStorageData = JSON.parse('{"__proto__": {"isAdmin": true}, "user": {"name": "attacker"}}');
+            
+            const result = helpers.extend(false, {}, localStorageData);
+
+            expect(result.user.name).toBe('attacker');
+
+            const testObj = {};
+            expect((testObj as any).isAdmin).toBeUndefined();
+        });
+
+        it('should protect against nested pollution attempts', () => {
+            const malicious = {
+                config: {
+                    settings: {
+                        __proto__: { polluted: true }
+                    }
+                }
+            };
+
+            const result = helpers.extend(true, {}, malicious);
+
+            expect(typeof result).toBe('object');
+            const testObj = {};
+            expect((testObj as any).polluted).toBeUndefined();
+        });
+
+        it('should handle mixed legitimate and malicious data', () => {
+            const mixed = {
+                validProp: 'valid',
+                __proto__: { isAdmin: true },
+                anotherValid: 123,
+                constructor: { polluted: true },
+                nested: {
+                    data: 'ok'
+                }
+            };
+
+            const result = helpers.extend(true, {}, mixed);
+
+            // Valid properties should be copied
+            expect(result.validProp).toBe('valid');
+            expect(result.anotherValid).toBe(123);
+            expect(result.nested.data).toBe('ok');
+
+            // Pollution should be blocked
+            const testObj = {};
+            expect((testObj as any).isAdmin).toBeUndefined();
+            expect((testObj as any).polluted).toBeUndefined();
+        });
+    });
+});
+
+