FreeScout: Stored XSS through SVG file upload with filter bypass

Summary

FreeScout is a free help desk and shared inbox built with PHP's Laravel framework. In versions 1.8.208 and below, bypasses of the attachment view logic and SVG sanitizer make it possible to upload and render an SVG that runs malicious JavaScript. An extension of .png with content type of image/svg+xml is allowed, and a fallback mechanism on invalid XML leads to unsafe sanitization. The application restricts which uploaded files are rendered inline: only files considered "safe" are displayed in the browser; others are served with Content-Disposition: attachment. This decision is based on two checks: the file extension (e.g. .png is allowed, while .svg may not be) and the declared Content-Type (e.g. image/* is allowed). By using a filename with an allowed extension (e.g. xss.png) and a Content-Type of image/svg+xml, an attacker can satisfy both checks and cause the server to treat the upload as a safe image and render it inline, even though the body is SVG and can contain scripted behavior. Any authenticated user can set up a specific URL, and whenever another user or administrator visits it, XSS can perform any action on their behalf. This issue has been fixed in version 1.8.209.