It is now recommended to disable whitelist checks of client HTTP headers in Shadow Daemon to prevent false-positives.
A HTTP client header is additional data that is passed to the web server by the client in a key-value format, for example self-identification as a specific browser through the user agent.
Historically the used headers were well defined and custom headers prefixed with
This changed in 2012 when RFC 6648 deprecated the
X- prefix and similar constructs.
Additionally, new headers are established by changes in the specification like Cross-Origin Resource Sharing, i.e. new clients may include new headers. It is expected that the servers ignore headers that they do not know and need.
The last years of running Shadow Daemon in production have shown that allowing all headers yields the best results in regards to false-positives/true-positives. If you are running Shadow Daemon as a web application firewall do not restrict the length or character set of the headers!
If you are running Shadow Daemon as a honeypot you may want to consider to continue using a very narrow list of allowed headers. Some malicious clients contain typos in header names and self-identify this way. I recommend to have a look at the results yourself here: https://demo.shadowd.zecure.org/parameters?parameter_filter%5BincludePaths%5D%5B0%5D=SERVER%7CHTTP_%2A¶meter_filter%5BincludeNoWhitelistRule%5D=1