Plane: Stored XSS via SVG attachment served inline on the application origin (account takeover)

Plane is an open-source project management tool. Prior to 1.4.0, an authenticated low-privilege workspace member, including a Guest, can upload an image/svg+xml file as a generic or issue attachment. The file retains the attacker-controlled Content-Type, and the asset-download endpoint creates a presigned URL with Content-Disposition: inline. In the default self-hosted MinIO deployment, the asset URL is served from the same origin as the Plane application, allowing embedded SVG JavaScript to execute in the application's security context. A victim, including a workspace administrator, who opens the link can have the session compromised through stored XSS, leading to account takeover. This issue is fixed in 1.4.0.