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    Activity Processors: Header Processor: Incident - Unexpected Request Header

    Complexity: Informational (0.0)

    Default Response: None

    Cause: WebApp Secure monitors all of the request headers included by clients. It has a list of known request headers that should be accepted. This list includes all of the headers defined in the HTTP RFC document, which means that if any additional headers are passed, it is part of some non standard HTTP extension. Should a user include a non standard header, this incident will be triggered. It is not necessarily a malicious action on its own, but it does signify that the client is unusual in some way (and potentially malicious) and therefore warrants additional monitoring.

    Behavior: When attackers are trying to exploit a server, one of the techniques is to attempt to profile what software the server is running. This can be partially accomplished by observing how the server reacts to various types of headers. For example, if the attacker knows that a specific 3rd party web application has a feature where it behaves differently if you send a header "X-No-Auth", then a hacker might send "X-No- Auth" to the site just to see what happens. While this could represent a higher level attack on a specific application; sending non standard headers is more likely part of the hacker's effort to scope the attack surface of the web site. This incident alone cannot be deemed malicious because some users have browser plug-ins installed that automatically include non standard headers with requests to some sites. Additionally, some AJAX sites also pass around custom headers as part of their expected protocol.

    Published: 2013-11-20