All versions of mckenziearts/livewire-markdown-editor prior to v1.3 contain a critical arbitrary file upload vulnerability in the MarkdownEditor::updatedAttachments() Livewire handler. The handler calls $file->store() with no server-side validation of MIME type, extension, or file content.
Any authenticated user with access to a page embedding <livewire:markdown-editor> can upload files of any type (.html, .svg, .js, .php, .exe, etc.) to the disk configured by livewire-markdown-editor.disk. When that disk is a public cloud bucket (S3, DigitalOcean Spaces, Cloudflare R2, Scaleway Object Storage — the common configuration when FILESYSTEM_DISK points to such a disk), uploaded files are served publicly with a guessed Content-Type header.
The consequences include:
Stored XSS on the storage domain via uploaded .html or .svg files
Phishing page hosting on the application's own storage domain (trust laundering)
Malware distribution from a domain users associate with the application
Markdown injection in the editor output via crafted filenames (the client-supplied getClientOriginalName() value was inserted verbatim into the markdown)
A real-world exploitation of this vulnerability was observed in production on a community platform using this package.
Patches
Upgrade to v1.3 or later.
Workarounds
If developers cannot upgrade immediately, disable the upload UI on every instance of the editor by passing :show-upload="false":