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If there is any header in the http request that contains the string 'host:' in their value before the actual host header the requests ends up being sent with two headers Host, the one specified by the user and the default one that's injected in case the header wasn't present.
$opts = array(
'header'=>"RandomHeader: localhost:8080\r\n" .
"Cookie: foo=bar\r\n" .
"Host: testcustomheader \r\n"
$context = stream_context_create($opts);
$fp = fopen('http://myserver.com', 'r', false, $context);
The raw headers should only contain the host header specified by the user that was sent in the context.
We get a faulty request with two Host headers instead:
GET / HTTP/1.0
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I dug into the source code to find out why this happens. This seems to be caused by an improper search of the Host: header to find out whether we should inject it or not.
Inside http_fopen_wrapper.c we use strstr to search an occurrence of the string 'host:' in the headers, and if that occurrence is in the beginning of a line then we set the have_header variable with HTTP_HEADER_HOST flag. If you try to send the Host header after another header that contains the string host: in the value of the header that flag won't be set and the default header will be injected.
A fix would be to check for every occurence of the host: string instead of just getting the first one.
The following pull request has been associated:
Patch Name: Fixes #79265: Improper injection of Host header when using fopen for http requests
On GitHub: https://github.com/php/php-src/pull/5201