Vulnerability Report: GO-2021-0226

• CVE-2020-24553
• Affects: net/http/cgi, net/http/fcgi
• Published: Jan 13, 2022
• Modified: Jun 12, 2023

When a Handler does not explicitly set the Content-Type header, the the package would default to “text/html”, which could cause a Cross-Site Scripting vulnerability if an attacker can control any part of the contents of a response. The Content-Type header is now set based on the contents of the first Write using http.DetectContentType, which is consistent with the behavior of the net/http package. Although this protects some applications that validate the contents of uploaded files, not setting the Content-Type header explicitly on any attacker-controlled file is unsafe and should be avoided.