Host-Header
The HTTP Host-Header response header is an unofficial HTTP header sent by some hosting providers and CDN backends to expose an MD5 hash identifying the hosting account or site configuration associated with the request.
Usage
On shared hosting infrastructure, many customer accounts share the same server resources. When Cloudflare proxies a request to an origin server, such as one running on SiteGround or a cPanel-based host, the origin returns a Host-Header value encoding which account owns the responding configuration.
The value is an MD5 hash derived from host configuration data on the origin server. Cloudflare passes the header through to the client response, where the hash becomes visible to anyone inspecting response headers. The hash allows hosting platform engineers to map a response back to a specific account or virtual host configuration during incident investigation.
The header name references the Host request header, the standard HTTP mechanism for indicating the target hostname. Despite the name similarity, Host-Header is a response header carrying a platform-specific identifier, not a reflection of the incoming Host request header value.
Values
MD5 account hash
The header value is a 32-character lowercase hexadecimal MD5 hash. The hash maps to a specific hosting account or virtual host configuration on the origin server's shared infrastructure.
Example
A response from a Cloudflare-proxied site using a cPanel-based hosting backend includes this header. The 32-character hex string is an MD5 hash identifying the origin hosting account. The value is stable for a given account configuration.
Host-Header: 6b7412fb82ca5edfd0917e3957f05d89
Different hosting accounts on the same server produce distinct hash values, allowing the hosting provider to route debug information and log entries to the correct account owner.
Takeaway
The Host-Header header carries an MD5 hash hosting providers use to identify the account or virtual host configuration on shared infrastructure. The value is meaningful only to the hosting platform and passes through CDN proxies to the final response.