Is content-encoding being set to UTF-8 invalid?

Question

Hi I have a client that is trying to POST to us with the following http headers:

content-type: application/x-www-form-urlencoded
content-encoding: UTF-8

But our web application firewall keeps picking them up and throwing error:

Message: [file "/etc/httpd/modsecurity.d/10_asl_rules.conf"] [line "45"] [id "340362"] [msg "Atomicorp.com WAF Rules: ModSecurity does not support content encodings and can not detect attacks using it, therefore it must be blocked."] [severity "WARNING"] Access denied with code 501 (phase 2). Match of "rx ^Identity$" against "REQUEST_HEADERS:Content-Encoding" required. Action: Intercepted (phase 2)

Anyone would like to shed some light into this matter?

Answer 1

It is invalid. The content-encoding specifies the data transfer encoding used by the issuer of the content. UTF-8 is not a content encoding, it is a character set. Specifying the character set is done in the content-type header:

content-type: text/plain; charset=utf-8

Valid content-encoding values are, for instance, gzip, deflate. An HTTP client should specify what content encoding it supports with the accept-encoding header; the HTTP server will reply with a content-encoding header.