1
 min read

X-Content-Type-Options Header Missing

The Anti-MIME-Sniffing header X-Content-Type-Options was not set to ‘nosniff’.

Summary

The Anti-MIME-Sniffing header X-Content-Type-Options was not set to ‘nosniff’. This allows older versions of Internet Explorer and Chrome to perform MIME-sniffing on the response body, potentially causing the response body to be interpreted and displayed as a content type other than the declared content type. Current (early 2014) and legacy versions of Firefox will use the declared content type (if one is set), rather than performing MIME-sniffing.

Solution

Ensure that the application/web server sets the Content-Type header appropriately and that it sets the X-Content-Type-Options header to 'nosniff' for all web pages. If possible, ensure that the end-user uses a standards-compliant and modern web browser that does not perform MIME-sniffing at all, or that can be directed by the web application/webserver to not perform MIME-sniffing.

References

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