> 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/web-cache-poisoning-via-unkeyed-query-string.md).
# Web Cache Poisoning via an Unkeyed Query String
Web Cache Poisoning via an Unkeyed Query String notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.
### Web Cache Poisoning via an Unkeyed Query String
This lab presents a vulnerability to poisoning of the web cache due to the fact that the **query string is not included in the cache key**. A legitimate user regularly visits the home page of the site using **Google Chrome**.
The objective is to poison the home page so that it returns a response containing a **JavaScript running `alert(1)`** in the victim's browser.
***
**Step 1: Home Page Interception**
The request to the site root (`/`) is intercepted. / In the response, we observe the presence of a canonical **link**, which indicates that some elements of the URL can be reflected in HTML.
***
**Step 2: Query string test**
An arbitrary query string is added to the URL:
```bash
/?test
```
The value is well **taken in the response**, which confirms that the query string influences the returned content.
**Step 3: HTML Injection**
The query string is then modified to inject HTML:
```bash
/?test'/>
JORDAN
```
The `
` tag is correctly interpreted by the browser, demonstrating a usable \*\* HTML injection\*\*.
**Step 4: JavaScript Injection (Cache poisoning)**
Replace the HTML injection with a JavaScript payload:
```bash
/?test'/>
```
The answer now contains the script, which is \*\* run by the browser\*\*.
**Result**
Since the query string is **not included in the cache key**, the poisoned response is stored and served to other users visiting the home page. / The victim then automatically triggers the execution of `alert(1)` during his visit, which validates the operation of the lab.
---
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