What is Nosniff?

The nosniff response header is a way to keep a website more secure. Security researcher Scott Helme describes it like this: “It prevents Google Chrome and Internet Explorer from trying to mime-sniff the content-type of a response away from the one being declared by the server.”

What is the use of Nosniff?

With the nosniff option, if the server says the content is text/html, the browser will render it as text/html. And you are done. The X-Content-Type-Options response HTTP header is a marker used by the server to indicate that the MIME types advertised in the Content-Type headers should not be changed and be followed.

What is Content-Type Nosniff?

The X-Content-Type-Options header is used to protect against MIME sniffing vulnerabilities. A response is sent back with the header X-Content-Type-Options: nosniff . This prevents the client from “sniffing” the asset to try and determine if the file type is something other than what is declared by the server.

What is MIME attack?

MIME sniffing vulnerabilities can occur when a website allows users to upload data to the server. The vulnerability comes into play when an attacker disguises an HTML file as a different file type (e.g. a JPEG, zip file, etc.). There are a couple of ways to avoid these kinds of attacks caused by MIME sniffing.

When to use nosniff on X Content Type?

X-Content-Type-Options: nosniff Directives nosniff Blocks a request if the request destination is of type: “style” and the MIME type is not text/css, or “script” and the MIME type is not a JavaScript MIME type; Enables Cross-Origin Read Blocking (CORB) protection for the MIME-types: text/html; text/plain

When to use nosniff to block a request?

nosniff Blocks a request if the requested type is 1. “style” and the MIME type is not “text/css”, or 2. “script” and the MIME type is not a JavaScript MIME type. Note: nosniff only applies to “script” and “style” types. Also applying nosniff to images turned out to be incompatible with existing web sites.

Why is there a nosniff option in Internet Explorer?

This header prevents Internet Explorer from MIME-sniffing a response away from the declared content-type as the header instructs the browser not to override the response content type. With the nosniff option, if the server says the content is text/html, the browser will render it as text/html.

When to opt out of MIME sniffing in nosniff?

This allows to opt-out of MIME type sniffing, or, in other words, it is a way to say that the webmasters knew what they were doing. nosniff Blocks a request if the requested type is 1. “style” and the MIME type is not “text/css”, or 2. “script” and the MIME type is not a JavaScript MIME type.