> 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/csrf/csrf-referer-validation-depends-on-header-presence.md).
# 仅在存在时进行 Referer 验证的 CSRF
### 当 Referer 验证依赖于头部存在时的 CSRF
此实验室的修改邮箱功能存在 CSRF 攻击漏洞。服务器尝试通过检查该请求头来阻止跨域请求， **Referer**但存在不安全的回退处理：当 Referer 头缺失时，会接受该请求。
* 推荐账户： `wiener:peter` （使用此账户从受害者的角度复现该场景。）
服务器检查 **Referer** 字段，以查明请求来自何处，并拒绝 Referer 不是本站点的请求。
* 通过从攻击服务器发送一个 POST 表单，返回结果： **“无效的 referer 头”** ——当头部存在且不正确时，该检查会生效。
```html
```
`“无效的 referer 头”`
不过，如果请求到达时 **不使用** referer 头缺失，服务器会接受该请求（危险的回退行为）。
#### 操作方法（原理）
1. 在利用服务器上托管一个页面，该页面会向 `/my-account/change-email` 提交一个带有攻击者邮箱的 POST 表单。
2. 强制让利用页面 **移除** 浏览器的 Referer 头，以便验证失败并作为拦截机制（因为服务器接受 Referer 缺失的情况）。
3. 让浏览器不发送 Referer 的一个简单方法是在利用页面中添加一个 `` 标签，然后再提交表单。
```html
```
---
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