ApostropheCMS is an open-source Node.js content management system. In versions up to and including 4.30.0, when `prettyUrls: true` is enabled on `@apostrophecms/file` (a documented SEO feature for serving uploaded files at clean URLs), the public pretty-URL handler builds the upstream URL using the raw `Host` HTTP request header. That URL is then `fetch`'ed and the response body + headers are streamed straight back to the requester. Because `Host` is fully attacker-controlled, an unauthenticated remote attacker can pivot the apostrophe process to issue outbound HTTP requests against any host it can reach on the private network. The path component is constrained to `/uploads/attachments/<cuid>-<slug>.<ext>` (built from a local-DB lookup), which keeps the impact narrow: cross-instance data exfiltration is neutralized by cuid uniqueness, but blind-SSRF residuals remain (network-topology mapping via response-code / timing differences and verbose proxy/WAF 404 body disclosure). As of time of publication, no known patched versions exist.

Affected: npm: apostrophe

### Summary

When `prettyUrls: true` is enabled on `@apostrophecms/file` (a documented SEO feature for serving uploaded files at clean URLs), the public pretty-URL handler builds the upstream URL using the raw `Host` HTTP request header:

```js proxyUrl = `${req.protocol}://${req.get('host')}${uglyUrl}` ```

That URL is then `fetch`'ed and the response body + headers are streamed straight back to the requester. Because `Host` is fully attacker-controlled, an **unauthenticated remote** attacker can pivot the apostrophe process to issue outbound HTTP requests against any host it can reach on the private network. The path component is constrained to `/uploads/attachments/<cuid>-<slug>.<ext>` (built from a local-DB lookup), which keeps the impact narrow: cross-instance data exfiltration is neutralised by cuid uniqueness, but blind-SSRF residuals remain (network-topology mapping via response-code / timing differences and verbose proxy/WAF 404 body disclosure). Verified on `apostrophe@4.30.0` (latest); no fixed release exists.

- **Affected:** `apostrophe <= 4.30.0` when `@apostrophecms/file` is configured with `prettyUrls: true` and uploadfs is **local** (the default; S3/CDN deployments produce an absolute `uglyUrl` and are not affected).

### Details

`modules/@apostrophecms/file/index.js` (excerpt; the public GET route registered when `prettyUrls: true`):

```js if (!self.options.prettyUrls) return; return { get: { async [`${self.options.prettyUrlDir}/*`](req, res) {…