[Stored XSS] Sync-In

Sync-In is a popular open-source file manager used by many individuals and teams. While exploring its features, I decided to test its security by attempting an XSS (Cross-Site Scripting) attack on the publicly available demo instance.

Steps to Reproduce:

1. Access the Demo Instance

      I started by accessing the official demo at https://demo.sync-in.com and logging in using the provided test credentials.

2. Upload an SVG File

      Next, I attempted to upload an SVG file containing embedded JavaScript. The upload was successful.

3. Render the SVG

      When I opened the file within the application, the SVG was rendered as an image, but the embedded script did not execute.

4. Open in New Tab

      Curious, I opened the rendered SVG image in a new browser tab.

5. XSS Triggered

      Once opened directly in a new tab, the embedded JavaScript executed, confirming the XSS vulnerability.


Outcome

I immediately reported the issue to the Sync-In team, who responded quickly and released a patch.

The vulnerability was resolved in v1.9.3. You can find the patch here:

https://github.com/Sync-in/server/releases/tag/v1.9.3

As a token of appreciation, I received a €50 bounty for my findings.

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