# Special HTTP headers

## Wordlists:

* [https://github.com/danielmiessler/SecLists/tree/master/Miscellaneous/web/http-request-headers](https://github.com/danielmiessler/SecLists/tree/master/Miscellaneous/web/http-request-headers)

## Headers to Change Location

Rewrite **IP source**:

* `X-Originating-IP: 127.0.0.1` 
* `X-Forwarded-For: 127.0.0.1`
* `X-Forwarded:  127.0.0.1`
* `Forwarded-For: 127.0.0.1`
* `X-Remote-IP: 127.0.0.1` 
* `X-Remote-Addr: 127.0.0.1`
* `X-ProxyUser-Ip: 127.0.0.1`
* `X-Original-URL: 127.0.0.1`
* `Client-IP: 127.0.0.1`
* `True-Client-IP: 127.0.0.1`
* `Cluster-Client-IP: 127.0.0.1`
* `X-ProxyUser-Ip: 127.0.0.1`
* `Connection: close, X-Forwarded-For` \(Check hop-by-hop headers\)

Rewrite **location**:

* `X-Original-URL: /admin/console`
* `X-Rewrite-URL: /admin/console`

## Hop-by-Hop headers

A hop-by-hop header is a header which is designed to be processed and consumed by the proxy currently handling the request, as opposed to an end-to-end header.

* `Connection: close, X-Forwarded-For`

{% page-ref page="../../pentesting-web/abusing-hop-by-hop-headers.md" %}

## HTTP Request Smuggling

* `Content-Length: 30`
* `Transfer-Encoding: chunked`

{% page-ref page="../../pentesting-web/http-request-smuggling.md" %}

## Cache Headers

* **`X-Cache`** in the response may have the value **`miss`** when the request wasn't cached and the value **`hit`** when it is cached
* **`Cache-Control`** indicates if a resource is being cached and when will be the next time the resource will be cached again: `Cache-Control: public, max-age=1800`
*  **`Vary`** is often used in the response to **indicate additional headers** that are treated as **part of the cache key** even if they are normally unkeyed.
* **`Age`** defines the times in seconds the object has been in the proxy cache.

{% page-ref page="../../pentesting-web/cache-deception.md" %}

## Conditionals

* Requests using these headers: `If-Modified-Since` and `If-Unmodified-Since` will be responded with data only if the response header`Last-Modified` contains a different time.
* Conditional requests using `If-Match` and `If-None-Match` use an Etag value so the web server will send the content of the response if the data \(Etag\) has changed. The `Etag` is taken from the HTTP response.
  * The **Etag** value is usually **calculated based** on the **content** of the response. For example, `ETag: W/"37-eL2g8DEyqntYlaLp5XLInBWsjWI"` indicates that the `Etag` is the **Sha1** of **37 bytes**.

## Range requests

* `Accept-Ranges`: Indicates if the server supports range requests, and if so in which unit the range can be expressed.
* `Range`: Indicates the part of a document that the server should return.
* `If-Range`: Creates a conditional range request that is only fulfilled if the given etag or date matches the remote resource. Used to prevent downloading two ranges from incompatible version of the resource.
* `Content-Range`: Indicates where in a full body message a partial message belongs.

## Message body information

* `Content-Length`**:** The size of the resource, in decimal number of bytes.
* `Content-Type`: Indicates the media type of the resource
* `Content-Encoding`: Used to specify the compression algorithm.
* `Content-Language`: Describes the human language\(s\) intended for the audience, so that it allows a user to differentiate according to the users' own preferred language.
* `Content-Location`: Indicates an alternate location for the returned data.

From a pentest point of view this information is usually "useless", but if the resource is **protected** by a 401 or 403 and you can find some **way** to **get** this **info**, this could be **interesting.**   
For example a combination of **`Range`** and **`Etag`** in a HEAD request can leak the content of the page via HEAD requests:

* A request with the header `Range: bytes=20-20` and with a response containing `ETag: W/"1-eoGvPlkaxxP4HqHv6T3PNhV9g3Y"` is leaking that the SHA1 of the byte 20 is `ETag: eoGvPlkaxxP4HqHv6T3PNhV9g3Y`

## Resources

* [https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers)