The vulnerability lies in the @apostrophecms/file component, where setting prettyUrls to true causes the system to build an upstream URL from the raw Host request header and then fetch that URL. The response body and headers are streamed directly back to the requester, allowing an unauthenticated attacker to direct the server to make outbound HTTP requests to any host it can reach. The path component is limited to /uploads/attachments/<cuid>-<slug>.<ext>, which restricts the attack surface to a single attachment path, but the attacker can still discover internal network topology, timing information, and receive verbose proxy/WAF responses, constituting a blind SSRF exposure. This weakness is classified as CWE‑918.

ApostropheCMS, the open-source Node.js content management system, is affected. Versions up to and including 4.30.0 expose this flaw when @apostrophecms/file’s prettyUrls feature is enabled. No patched versions are currently available.

The CVSS score of 3.7 indicates a low overall severity, and the EPSS score is not provided. The vulnerability is not listed in the CISA KEV catalog. Because the attack requires only an unauthenticated HTTP request with a crafted Host header, the likelihood of exploitation is low but not negligible; the attacker must also have access to the network segment that the ApostropheCMS server can reach. No confirmed exploits are known yet, but the blind SSRF can still be useful for reconnaissance of internal hosts.