It is common practice for the same web server to host several websites or web applications on the same IP address. This why the host header exists. The host header specifies which website or web application should process an incoming HTTP request. The web server uses the value of this header to dispatch the request to the specified website or web application.
Each web application hosted on the same IP address is commonly referred to as a virtual host. So what constitutes a host header attack? What happens if we specify an invalid Host Header? Most web servers are configured to pass the unrecognized host header to the first virtual host in the list. Another way to pass arbitrary Host headers is to use the X-Forwarded-Host header. In some configurations this header will rewrite the value of the Host header.
Unfortunately, what many application developers do not realize is that the HTTP host header is controlled by the user. As you might already know, in application security user input should always be considered unsafe and therefore, never trusted without properly validating it first.
The PHP script in the following example is a typical and dangerous use of the host header. An attacker can potentially manipulate the code above to produce the following HTML output just by manipulating the host header.
The two major attack vectors host header attacks enable are web-cache poisoning, and abuses of alternative channels for conducting sensitive operations, such as password resets. Web-cache poisoning is a technique used by an attacker to manipulate a web-cache to serve poisoned content to anyone who requests pages. For this to occur, an attacker would need to poison a caching proxy run by the site itself, or downstream providers, content delivery networks CDNssyndicators or other caching mechanisms in-between the client and the server.
The cache will then serve the poisoned content to anyone who request it, with the victim having no control whatsoever on the malicious content being served to them. The below is an example of how an attacker could potentially exploit a host header attack by poisoning a web-cache. A common way to implement password reset functionality is to generate a secret token and send an email with a link containing this token. What could happen if an attacker requests a password reset with an attacker controlled host header?
If the web application makes use of the host header value when composing the reset link, an attacker can poison the password reset link that is sent to a victim. Acunetix solves this by making use of AcuMonitor as its intermediary service during an automated scan. During a scan, Acunetix will locate the password reset page and inject a custom host header pointing to an AcuMonitor domain.
If vulnerable, the application in question an old version of Piwik in this example will generate the password reset link using this value and send an email to the user concerned as follows. However in some cases, this is easier said than done especially situations involving legacy code. One of the properties that you can configure is the Host Name to use. The recommendation is completely wrong and may only make the situation worse. Do you not realize that will cause the internal name of a server to be reflected out to the client?
Host header attacks are attacks on the web application or the caching proxy server. They cannot be solved from the server IIS in this case itself. Web-cache poisoning Web-cache poisoning is a technique used by an attacker to manipulate a web-cache to serve poisoned content to anyone who requests pages.
Connected to www. Password Reset Poisoning A common way to implement password reset functionality is to generate a secret token and send an email with a link containing this token. Get the latest content on web security in your inbox each week.For example, assume that you have a web application that serves localized web pages.
The web application determines the language for the response based on the HTTP cookie in the request.
The problem with this approach is that search engines will not index the localized content of this application, because search engine crawlers do not use HTTP cookies and hence only the content in default language will be served by the web application. To setup the walkthrough scenario copy the following ASP. By default, the distributed rewrite rules i.
For this walkthrough you will need to add the following two server variables to the "Allowed Server Variables" list:. It is not necessary to add a server variable to the "Allowed" list if that server variable is set by using a global rewrite rule.
Use the "Add After the "Allowed Server Variables" list has been updated, click "Back to Rules" action to go back to the rules list view. The next step is to define a rewrite map that will be used to map the URL part, representing the language to the locale identifier that will be saved by the rewrite rule into the HTTP cookie header. This map will define mappings between the URL part that represents a language and the locale identifier to be used when setting the HTTP request cookie.
Click "Edit Map Settings Close the dialog and then use the "Add Mapping Entry Finally, you will create a rewrite rule that sets the server variables by using the rewrite map defined earlier. Bring up the "Edit Rule" dialog by clicking on the "Add Rules Enter the rule configuration as below:. It also captures the language segment and the remainder of the URL path in the rule back-references, so that they can be re-used later in the rule.
The rule condition uses the previously captured language segment as a lookup key that is passed to the rewrite map "Languages". The result of the map lookup is stored in the condition back-reference. The rule action rewrites the URL to not contain the language segment. Expand the "Server Variables The HTTP cookie is set by using the condition back-reference, which contains the locale identifier obtained from the "Languages" rewrite map.A question can only have one accepted answer.
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DigitalOcean Meetups Find and meet other developers in your city. I have a application with front end as angular js and api in node. Lately, i am unable to use anything due to CORS policy issue. I tried adding permission in apache virtual hostbut nothing seems to be working. Following is the issue statement visible in console. Please help. Add comments here to get more clarity or context around a question.
These answers are provided by our Community. If you find them useful, show some love by clicking the heart. If you run into issues leave a comment, or add your own answer to help others. Update Apache config to dynamically mirror the port of the requesting origin. Thank you so much for such a elaborate explanation.
I really appreciate it. Kindly suggest if i am doing something wrong. You can type! I have a website it's the only site hosted on the droplet and sometimes about 1 time each month, but not on the same day the CPU usage goes through the roof.
I have absolutely no idea what's causing it, but in 1 minute the CPU usage goes from How do we use a GUI to manage the database? I tried using RoboMongo and MongoChef but neither works.
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Replace previous answer? Yes, I'm sure.This header is required if the request has an Access-Control-Request-Headers header. Here's an example of what an Access-Control-Allow-Headers header might look like.
This example shows Access-Control-Allow-Headers when it specifies support for multiple headers. Although CORS-safelisted request headers are always allowed and don't usually need to be listed in Access-Control-Allow-Headerslisting them anyway will circumvent the additional restrictions that apply. Let's look at an example of a preflight request involving Access-Control-Allow-Headers.
First, the request. Get the latest and greatest from MDN delivered straight to your inbox. Sign in to enjoy the benefits of an MDN account. The compatibility table in this page is generated from structured data. Last modified: Apr 12,by MDN contributors. Related Topics. Sites can use this to avoid clickjacking attacks, by ensuring that their content is not embedded into other sites.
If this value is absent, then any URI is allowed. For workers, non-compliant requests are treated as fatal network errors by the user agent. This is an enforcement on what navigations this document initiates not on what this document is allowed to navigate to. It applies restrictions to a page's actions including preventing popups, preventing the execution of plugins and scripts, and enforcing a same-origin policy.
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Sign in with Github Sign in with Google. Chrome Full support 4. Edge Full support Firefox Full support 3. IE Full support Opera Full support Safari Full support 4. WebView Android Full support 2. Chrome Android Full support Yes. Firefox Android Full support 4. Opera Android Full support Safari iOS Full support 3. Samsung Internet Android Full support Yes.For entity-header fields, both sender and recipient refer to either the client or the server, depending on who sends and who receives the entity.
The Accept request-header field can be used to specify certain media types which are acceptable for the response. Accept headers can be used to indicate that the request is specifically limited to a small set of desired types, as in the case of a request for an in-line image.
Setting HTTP request headers and IIS server variables
The media-range MAY include media type parameters that are applicable to that range. Each media-range MAY be followed by one or more accept-params, beginning with the "q" parameter for indicating a relative quality factor. The first "q" parameter if any separates the media-range parameter s from the accept-params. Quality factors allow the user or user agent to indicate the relative degree of preference for that media-range, using the qvalue scale from 0 to 1 section 3. If no Accept header field is present, then it is assumed that the client accepts all media types.
If an Accept header field is present, and if the server cannot send a response which is acceptable according to the combined Accept field value, then the server SHOULD send a not acceptable response. Media ranges can be overridden by more specific media ranges or specific media types.
If more than one media range applies to a given type, the most specific reference has precedence. For example. The media type quality factor associated with a given type is determined by finding the media range with the highest precedence which matches that type.
The Accept-Charset request-header field can be used to indicate what character sets are acceptable for the response.
This field allows clients capable of understanding more comprehensive or special- purpose character sets to signal that capability to a server which is capable of representing documents in those character sets. Character set values are described in section 3. Each charset MAY be given an associated quality value which represents the user's preference for that charset. An example is. If no Accept-Charset header is present, the default is that any character set is acceptable.
If an Accept-Charset header is present, and if the server cannot send a response which is acceptable according to the Accept-Charset header, then the server SHOULD send an error response with the not acceptable status code, though the sending of an unacceptable response is also allowed. The Accept-Encoding request-header field is similar to Accept, but restricts the content-codings section 3. A server tests whether a content-coding is acceptable, according to an Accept-Encoding field, using these rules:.
If an Accept-Encoding field is present in a request, and if the server cannot send a response which is acceptable according to the Accept-Encoding header, then the server SHOULD send an error response with the Not Acceptable status code. If no Accept-Encoding field is present in a request, the server MAY assume that the client will accept any content coding.
In this case, if "identity" is one of the available content-codings, then the server SHOULD use the "identity" content-coding, unless it has additional information that a different content-coding is meaningful to the client.
The Accept-Language request-header field is similar to Accept, but restricts the set of natural languages that are preferred as a response to the request. Language tags are defined in section 3. Each language-range MAY be given an associated quality value which represents an estimate of the user's preference for the languages specified by that range.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together.
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Already on GitHub? Sign in to your account. This would allow all non-simple headers passed in the request to be added to the browser's preflight cache. This si currently possible by simply mirroring back the value of the Access-Control-Request-Headers request header, but this would be much simpler. The browser would need to track the request headers passed and add them all to their preflight cache rather than simply parse them out from the Access-Control-Allow-Headers response header, assuming that's what they currently dobut that's not too hard to do.
Implementers have traditionally been wary about doing this, since it could be a footgun. Servers might have forgotten about side effects of certain request headers, etc.
But like Origindon't allow the wildcard when. Thanks, craigfrancisI concur. If we allow this of which I'm not completely convinced yetwe should disallow credentials in the wildcard case.
Of course, we should also disallow forbidden headers. Feetgun footguns? FWIW, there are many examples out on the internet some good, some bad of CORS implementations, but there is no 'reference implementation'. As for reference implementations, I'm not sure we have the bandwidth to maintain that, or are you volunteering? I'm personally also a little wary of writing both the specification and implementation as that leads to tunnel vision issues. So maybe in their code, they include a check for Origin, and if it's on their 'safe' list, they respond with:.
Or that if Access-Control-Allow-Credentials: true is specified in the response, then the browser must throw an error? The browsers will normally handle this as you would expect as a wildcardbut they will reject it when requesting a resource with. For any website that wants to allow this behaviour which is where the security risk comes inthey will need to replace the wildcard with a proper Origin, and provide the Access-Control-Allow-Credentials header as well, e.
So if we used the same logic with all 3 of these headers, then a response that contains the following should be fine:.
HTTP - Header Fields
That's consistent with how Access-Control-Allow-Origin currently works, and should be very safe and cover the common use cases. Reply to this email directly or view it on GitHub comment. New issue or PR for those would be appreciated. I also like the idea of extending wildcard support for the no-credentials scenario. But why should this limitation apply to specifying which request headers are allowed?
Headers aren't specific to a requesting domain like cookies. All this would do is tell the browser to allow all headers to be sent in the CORS request to the server without being specified individually - it's not a guarantee that the server will actually 'process' them. It's probably nice to add, simply to have some standardization across all the Access-Control-Allow request headers, but it's not a deal-breaker.
Getting W3C to acknowledge reality is going rather slow, see comment for progress on that. And as I noted in comment in a different but related thread, I think that a far greater percentage of CORS requests are credentialed than we might assume.
Websites quite often today simply set a x-xhr-request: true header as a CSRF prevention mechanism. To clarify. That's generally no different than what can be done from non-browser clients anyway.
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Viewed 31k times. Active Oldest Votes. There is a workaround but best solution is to rewrite the attribute to valid syntax. But when request is called from the android app it shows me undefined. Unfortunately, this has made no affect. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown.
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