# Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') (CWE-1321)

The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype.

**Stack:** JavaScript

- Prevalence: 中 覆盖 1 种语言
- Impact: 高 1 条严重级别为高的规则
- Prevention: 已记录 2 个修复示例

**OWASP:** Injection (A03:2021-Injection) - #3

## Description

By modifying the prototype of base objects like Object.prototype, attackers can affect all objects that inherit from these prototypes, potentially leading to code execution or denial of service.

## Prevention

基于 2 条 Shoulder 检测规则的 Prototype Pollution 预防策略。

### JavaScript

Filter dangerous keys (__proto__, constructor, prototype) or use schema validation before merging user input

Use Object.hasOwn() to verify authorization properties are own properties, not inherited from a polluted prototype

## Warning Signs

- [HIGH] user input flowing to object merge operations without filtering dangerous keys
- [MEDIUM] authorization checks that trust properties without verifying they are own properties

## Consequences

- 执行未授权代码
- 修改应用程序数据
- 拒绝服务 (DoS)

## Mitigations

- 对查找用对象使用 Object.create(null)
- 在为对象赋值前对键进行验证和净化
- 对用户可控的键使用 Map 而不是普通对象

## Detection

- Total rules: 2
- Languages: javascript, typescript

## Rules by Language

### Javascript (2 rules)

- **Prototype Pollution via Object Manipulation** [HIGH]: Detects user input flowing to object merge operations without filtering dangerous keys.
  - Remediation: Filter dangerous keys (__proto__, constructor, prototype) before merging objects.

```javascript
const BLOCKED = ['__proto__', 'constructor', 'prototype'];
const filtered = Object.fromEntries(
  Object.entries(input).filter(([k]) => !BLOCKED.includes(k))
);
```

Learn more: https://shoulder.dev/learn/javascript/cwe-1321/prototype-pollution
- **Prototype Pollution Gadget - Unsafe Property Trust** [MEDIUM]: Detects authorization checks that trust properties without verifying they are own properties.
  - Remediation: Use Object.hasOwn() to verify properties are not inherited from prototype.

```javascript
if (Object.hasOwn(user, 'isAdmin') && user.isAdmin) {
  grantAccess();
}
```

Learn more: https://shoulder.dev/learn/javascript/cwe-1321/prototype-pollution-gadget

### Typescript (2 rules)

- **Prototype Pollution via Object Manipulation** [HIGH]: Detects user input flowing to object merge operations without filtering dangerous keys.
  - Remediation: Filter dangerous keys (__proto__, constructor, prototype) before merging objects.

```javascript
const BLOCKED = ['__proto__', 'constructor', 'prototype'];
const filtered = Object.fromEntries(
  Object.entries(input).filter(([k]) => !BLOCKED.includes(k))
);
```

Learn more: https://shoulder.dev/learn/javascript/cwe-1321/prototype-pollution
- **Prototype Pollution Gadget - Unsafe Property Trust** [MEDIUM]: Detects authorization checks that trust properties without verifying they are own properties.
  - Remediation: Use Object.hasOwn() to verify properties are not inherited from prototype.

```javascript
if (Object.hasOwn(user, 'isAdmin') && user.isAdmin) {
  grantAccess();
}
```

Learn more: https://shoulder.dev/learn/javascript/cwe-1321/prototype-pollution-gadget