Restricting node access based on the Host hypertext transfer protocol header to fix the host header vulnerability where exploiter exploit horde hypertext transfer protocol header .

Send ambiguous requests

The code that validates the host and the code that does something vulnerable with it often reside in different application components or tied on branch servers. By identifying and exploiting discrepancies in how they retrieve the Host header, you may be able to issue an ambiguous request that appears to have a different server depending on which system is looking at it .
The follow are barely a few examples of how you may be able to create ambiguous requests .

Inject duplicate Host headers

One potential approach is to try adding twin Host headers. true, this will frequently merely result in your request being blocked. however, as a browser is improbable to always send such a request, you may occasionally find that developers have not anticipated this scenario. In this case, you might expose some interest behavioral quirks.

different systems and technologies will handle this shell differently, but it is common for one of the two headers to be given priority over the early one, efficaciously overriding its respect. When systems disagree about which header is the correct one, this can lead to discrepancies that you may be able to exploit. Consider the surveil request :
GET /example HTTP/1.1
Host: bad-stuff-here

Let ’ s say the front-end gives priority to the first gear case of the header, but the back-end prefers the final examination exemplify. Given this scenario, you could use the first header to ensure that your request is routed to the intended target and use the second header to pass your cargo into the server-side code .

Supply an absolute URL

Although the request course typically specifies a relative path on the requested domain, many servers are besides configured to understand requests for absolute URLs .
The ambiguity caused by supplying both an absolute URL and a Host header can besides lead to discrepancies between unlike systems. officially, the request line should be given precedence when routing the request but, in practice, this international relations and security network ’ t always the lawsuit. You can potentially exploit these discrepancies in much the lapp way as duplicate Host headers .
Host: bad-stuff-here

note that you may besides need to experiment with different protocols. Servers will sometimes behave differently depending on whether the request channel contains an HTTP or an HTTPS URL .

Add line wrapping

You can besides uncover far-out behavior by indenting HTTP headers with a space character. Some servers will interpret the indent header as a wind line and, consequently, treat it as separate of the preceding header ’ s value. early servers will ignore the indent header raw .
due to the highly inconsistent cover of this case, there will often be discrepancies between different systems that process your request. For model, consider the adopt request :
GET /example HTTP/1.1
 Host: bad-stuff-here

The web site may block requests with multiple Host headers, but you may be able to bypass this establishment by indenting one of them like this. If the front-end ignores the indent header, the request will be processed as an average request for now let ’ s say the back-end ignores the leading space and gives precession to the first header in the case of duplicates. This discrepancy might allow you to pass arbitrary values via the “ wrapped ” Host header .

Other techniques

This is just a belittled sample of the many possible ways to issue harmful, equivocal requests. For example, you can besides adapt many HTTP request smuggling techniques to construct Host header attacks. We ’ ll cover this in more detail in our dedicated request smuggling subject.

Inject host override headers

even if you can ’ thymine override the Host header using an equivocal request, there are early possibilities for overriding its value while leaving it entire. This includes injecting your warhead via one of several other HTTP headers that are designed to serve just this purpose, albeit for more innocent use cases .
As we ’ ve already discussed, websites are often accessed via some kind of mediator system, such as a load halter or a inverse proxy. In this kind of computer architecture, the Host header that the back-end server receives may contain the knowledge domain name for one of these mediator systems. This is normally not relevant for the request functionality .
To solve this problem, the front-end may inject the X-Forwarded-Host header, containing the original prize of the Host header from the node ’ s initial request. For this cause, when an  X-Forwarded-Host header is deliver, many frameworks will refer to this alternatively. You may observe this demeanor evening when there is no front-end that uses this heading .
You can sometimes use X-Forwarded-Host to inject your malicious input signal while circumventing any establishment on the Host heading itself .
GET /example HTTP/1.1
X-Forwarded-Host: bad-stuff-here

For Environments like below

  • Red Hat Enterprise Linux
  • Red Hat JBoss Enterprise Application Platform (EAP)
    • 6
    • 7
  • Red Hat JBoss Web Server
  • JBoss Core Services

For httpd, you can use a RewriteRule like under. This exemplar dominion would only allow and

RewriteEngine On
RewriteCond %{HTTP_HOST} !^(|$ [NC]
RewriteRule .* - [F]

If you need to restrict X-Forwarded-Host headers allowed because httpd is behind a proxy, then you may use a rule like the follow :
Note: This rewrite rule will be same for IBM Http Server, Redhat httpd server, Redhat hat web Server, OHS …etc

RewriteEngine On
RewriteCond %{HTTP:X-Forwarded-Host} !^$ [NC]
RewriteCond %{HTTP:X-Forwarded-Host} !^(|$ [NC]
RewriteRule .* - [F]

For JBoss EAP 7, use an expression-filter in the Undertow subsystem :

/subsystem=undertow/configuration=filter/expression-filter=host-checker:add(expression="not(equals(%{i,Host}, or equals(%{i,Host}, -> response-code(403)")

The result XML would look like this


For JBoss EAP 6, use a rewrite in the JBoss Web subsystem :

reservoir :
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