[release-branch.go1.19] html/template: emit filterFailsafe for empty unquoted attr value

An unquoted action used as an attribute value can result in unsafe
behavior if it is empty, as HTML normalization will result in unexpected
attributes, and may allow attribute injection. If executing a template
results in a empty unquoted attribute value, emit filterFailsafe

Thanks to Juho Nurminen of Mattermost for reporting this issue.

For #59722
Fixes #59815
Fixes CVE-2023-29400

Change-Id: Ia38d1b536ae2b4af5323a6c6d861e3c057c2570a
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/1826631
Reviewed-by: Julie Qiu <julieqiu@google.com>
Run-TryBot: Roland Shoemaker <bracewell@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/1851498
Reviewed-by: Roland Shoemaker <bracewell@google.com>
Run-TryBot: Damien Neil <dneil@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/491357
Run-TryBot: Carlos Amedee <carlos@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
3 files changed
tree: 9dfe6eeeaf058936227370468327d6bc67ed878b
  1. .github/
  2. api/
  3. doc/
  4. lib/
  5. misc/
  6. src/
  7. test/
  8. .gitattributes
  9. .gitignore
  10. codereview.cfg
  14. README.md
  15. SECURITY.md

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