- Allowlist inline MIME types (png/jpeg/gif/webp/pdf only); everything
else, including SVG and HTML, served as application/octet-stream
with content-disposition: attachment.
- X-Content-Type-Options: nosniff and a restrictive CSP on every response.
- Validate the upstream URL Civi returns: must match CIVI_BASE_URL origin
before we attach basic-auth creds and follow it. redirect: manual to
prevent off-host hops.
- Drop SVG from the client's inline-image list (server forces download).
Joel Brock