[release-branch.go1.15-security] 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 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>
(cherry picked from commit 23d675d07fdc56aafd67c0a0b63d5b7e14708ff0)
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/835311
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
5 files changed
tree: 22816017d9892e7a0ee0382e8db61d4c27525829
  1. .github/
  2. api/
  3. doc/
  4. lib/
  5. misc/
  6. src/
  7. test/
  8. .gitattributes
  9. .gitignore
  13. favicon.ico
  16. README.md
  17. robots.txt
  18. SECURITY.md

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