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    Activity Processors: Header Processor: Incident - Missing User Agent Header

    Complexity: Low (2.0)

    Default Response: 1x = Slow Connection 2-6 seconds and Captcha.

    Cause: Most legitimate web browsers and tools submit a User-Agent header with each HTTP request. The user agent header contains information that identifies which software the user is using to access the website, whether that software it is Googlebot, Firefox, Safari, or another piece of software. If a user submits a request that does not contain a User-Agent header, this incident will be triggered.

    Behavior: Not providing a user-agent header is generally an activity performed trying to evade detection. The user agent header provides identifying information that could be used by the webserver to track requests made by the same user. It can also provide information about the user's personal computer. Sometimes, hackers will replace the user agent string with another user agent string that is perfectly legitimate, but for a different environment than the one they are actually using. Some legitimate users also take this measure as a general security practice; therefore, as long as at least some value is submitted for the user-agent, it cannot be guaranteed to be a malicious act. However, in the case of the header being absent, a user would have had to take advantage of a tool or debugging proxy in order to filter the traffic. This is almost always performed during the course of a malicious action. Some tools such as network heath monitors can also trigger this incident, because they are doing something normal users should not do, but they are considered trusted. In this case, the IP addresses of those tools should be added to the configuration trusted IP whitelist.

    Published: 2014-06-27