livewire-markdown-editor has arbitrary file upload that allows stored XSS via attachment handler

Impact

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":

  <livewire:markdown-editor wire:model="content" :show-upload="false" />

This hides the file input and prevents the vulnerable code path from being reached.

Resources

• Patch commit: https://github.com/mckenziearts/livewire-markdown-editor/pull/12
• Release: https://github.com/mckenziearts/livewire-markdown-editor/releases/tag/v1.3
• CWE-434: https://cwe.mitre.org/data/definitions/434.html
• CWE-79: https://cwe.mitre.org/data/definitions/79.html