net/http/cgi,net/http/fcgi: add Content-Type detection

This CL ensures that responses served via CGI and FastCGI
have a Content-Type header based on the content of the
response if not explicitly set by handlers.

If the implementers of the handler did not explicitly
specify a Content-Type both CGI implementations would default
to "text/html", potentially causing cross-site scripting.

Thanks to RedTeam Pentesting GmbH for reporting this.

Fixes #40928
Fixes CVE-2020-24553

Change-Id: I82cfc396309b5ab2e8d6e9a87eda8ea7e3799473
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/823217
Reviewed-by: Russ Cox <rsc@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/252179
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>
5 files changed
tree: 9aba6fa0d87f10f1cf442a95a6c9e6f1200d28fb
  1. .github/
  2. api/
  3. doc/
  4. lib/
  5. misc/
  6. src/
  7. test/
  8. .gitattributes
  9. .gitignore
  10. AUTHORS
  11. CONTRIBUTING.md
  12. CONTRIBUTORS
  13. favicon.ico
  14. LICENSE
  15. PATENTS
  16. README.md
  17. robots.txt
  18. SECURITY.md
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