Upload safety

Every name and type that reaches storage is treated as untrusted:

• The mime type is sniffed from the bytes (ext-fileinfo) — never taken from the client, a remote Content-Type header or a disk’s stored metadata.
• The stored name is one safe path segment. Directory parts, separators and control characters are stripped from a client’s name and from usingFileName(), so a name can never reach outside the media’s own directory.
• The extension can’t lie about active content. An extension a web server may execute (.php, .phtml, .shtml, …) is never stored, and one a browser runs (.html, .svg, .js, …) is kept only when the bytes really are that type — a PNG uploaded as x.html is stored as x.png. Truthful or harmless extensions (IMG_0001.JPG, data.csv) are kept.
• addFromUrl() only fetches http/https URLs, and it is safe to hand a user’s URL — it shares its guard with MediaLibrary::remote() (see Remote URLs). Every hop is canonicalised and rebuilt (user info, numeric IPv4 spellings, a backslash or % in the host and IPv6 zone ids are refused), and a host that is, resolves to or redirects to a private, loopback, link-local (cloud metadata), carrier-grade NAT or other reserved address — IPv4 or IPv6 — or is localhost is refused before any request to it (SSRF). Redirects are followed by hand (media.remote.max_redirects, five by default), each hop vetted the same way, and every host name is resolved once and the connection pinned to every vetted address, bypassing the environment’s proxy, so a second DNS answer can’t swap in an internal one.
• media.remote.headers go to the URL’s own origin only — a redirect to another origin doesn’t receive them unless media.remote.forward_headers_on_redirect is on — and media.remote.timeout is one budget for the whole download, every hop included.
• Trusted internal hosts go in media.remote.allowed_private_hosts (exact host names, addresses or address/prefix ranges); media.remote.block_private_networks => false turns the guard off — only for URLs you trust completely. Pinning needs ext-curl: without it a host name is refused, while address literals and allowlisted host names still work. An internationalised or punycode (xn--) host name needs ext-intl; without it, it is refused.
• A remote download streams to disk and stops the moment it passes the size cap, counting decoded bytes, with or without a Content-Length. Every refusal throws RemoteFileRejected; a non-2xx answer throws FileDoesNotExist, and a transport failure surfaces as Laravel’s ConnectionException.
• Images are measured from their header before anything is decoded: one over media.max_image_pixels (50 megapixels by default) is stored without variants or placeholders, so a tiny file declaring a huge canvas can’t exhaust memory. SVG is never decoded on the server — see Image variants.
• A bucket without acceptsMimeTypes() accepts any type, HTML and SVG included. Give every bucket that holds user uploads an allowlist.

Serving is hardened the same way — see URLs, streaming & downloads for which types the streaming route serves inline, and why private media needs a private disk.