Staff file proxy: harden against SVG XSS and SSRF

- 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).

app/api/staff/file/route.ts

@@ -67,6 +67,25 @@ export async function GET(req: NextRequest) {
       return new NextResponse("Not found", { status: 404 });
     }
 
+    // SSRF guard: only follow URLs whose origin matches CIVI_BASE_URL. Civi
+    // returns absolute URLs for attachments; if a compromised Civi (or DB row
+    // tamper) ever set this to an attacker-controlled host, the basic-auth
+    // creds attached below would leak. Validating the origin closes that.
+    const civiOrigin = new URL(process.env.CIVI_BASE_URL!).origin;
+    let upstreamUrl: URL;
+    try {
+      upstreamUrl = new URL(row.url);
+    } catch {
+      console.error(`[staff/file] malformed civi url id=${id}`);
+      return new NextResponse("Upstream error", { status: 502 });
+    }
+    if (upstreamUrl.origin !== civiOrigin) {
+      console.error(
+        `[staff/file] refused cross-origin upstream id=${id} origin=${upstreamUrl.origin}`,
+      );
+      return new NextResponse("Upstream error", { status: 502 });
+    }
+
     const headers: Record<string, string> = {};
     if (process.env.CIVI_HTTP_AUTH_USER && process.env.CIVI_HTTP_AUTH_PASS) {
       const creds = Buffer.from(
@@ -75,7 +94,7 @@ export async function GET(req: NextRequest) {
       headers["Authorization"] = `Basic ${creds}`;
     }
 
-    const upstream = await fetch(row.url, { headers });
+    const upstream = await fetch(upstreamUrl, { headers, redirect: "manual" });
     if (!upstream.ok || !upstream.body) {
       console.error(
         `[staff/file] upstream fetch failed: id=${id} status=${upstream.status}`,
@@ -83,15 +102,29 @@ export async function GET(req: NextRequest) {
       return new NextResponse("Upstream error", { status: 502 });
     }
 
-    const safeName = (row.name || `file-${id}`).replace(/"/g, "");
-    const mime = row.mime_type || upstream.headers.get("content-type") || "application/octet-stream";
-    const isInline = mime.startsWith("image/") || mime === "application/pdf";
+    // XSS guard: only allow a fixed allowlist of MIME types to render inline
+    // (browsers execute scripts inside SVGs and HTML, and will sniff some
+    // ambiguous types). Everything else is forced to attachment with a
+    // neutralised content-type. nosniff blocks MIME sniffing entirely.
+    const SAFE_INLINE = new Set([
+      "image/png",
+      "image/jpeg",
+      "image/gif",
+      "image/webp",
+      "application/pdf",
+    ]);
+    const safeName = (row.name || `file-${id}`).replace(/[\r\n"]/g, "");
+    const declaredMime = row.mime_type || upstream.headers.get("content-type") || "application/octet-stream";
+    const isInline = SAFE_INLINE.has(declaredMime);
+    const servedMime = isInline ? declaredMime : "application/octet-stream";
     return new NextResponse(upstream.body, {
       status: 200,
       headers: {
-        "content-type": mime,
+        "content-type": servedMime,
         "content-disposition": `${isInline ? "inline" : "attachment"}; filename="${safeName}"`,
         "cache-control": "private, max-age=60",
+        "x-content-type-options": "nosniff",
+        "content-security-policy": "default-src 'none'; sandbox; style-src 'unsafe-inline'",
       },
     });
   } catch (e) {