Host-Header
The HTTP Host-Header response header is an unofficial header sent by WordPress-focused hosting platforms, exposing an identifier for the platform or hosting tier serving the request.
Usage
WordPress hosting platforms attach
Host-Header to responses from their shared
infrastructure. Some values name the platform or
hosting tier, the MD5 hash of wpvip on
Automattic's WordPress VIP and Base64 tier names on
Bluehost, while the two most widespread hash values
travel with cPanel and LiteSpeed shared-hosting
stacks and vary between URLs on the same site, so
their derivation stays unconfirmed. The header
survives any CDN in front
of the origin and reaches clients, exposing hosting
details to anyone inspecting
response headers.
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 identifier, not a reflection of the incoming Host request header value.
Values
Crawl data shows three value shapes, each tied to a platform family.
MD5-style hash
A 32-character lowercase hexadecimal value. The hash
of wpvip appears
across Automattic's WordPress VIP infrastructure.
Two further hash values dominate cPanel and
LiteSpeed shared hosting, spanning dozens to
hundreds of hostnames while varying between URLs on
a single site, so no label deriving them has been
confirmed.
Base64 hosting tier
A Base64-encoded hostname naming a Bluehost tier:
c2hhcmVkLmJsdWVob3N0LmNvbQ== decodes to
shared.bluehost.com and
Y2xvdWQuYmx1ZWhvc3QuY29t decodes to
cloud.bluehost.com.
Plain platform label
A readable label such as WordPress.com or
wpcloud, naming the Automattic platform serving
the response.
Example
A response from WordPress VIP infrastructure
carries the platform hash, the MD5 of wpvip. The
same value appears across the sites the tier
serves, from news publishers to universities.
Host-Header: a9130478a60e5f9135f765b23f26593b
A Bluehost-hosted site reveals its hosting tier through the Base64 form.
Host-Header: c2hhcmVkLmJsdWVob3N0LmNvbQ==
