livewire-markdown-editor has arbitrary file upload that allows stored XSS via attachment handler
Date: 2026-05
Affected: composer/mckenziearts/livewire-markdown-editor
Attack vector: xss
Category: vulnerability-disclosure
Severity: High
CWE: CWE-434
CWE-79
CVSS: 7.1 (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:N)

### 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 pass


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Architectural layers (MAESTRO):