GitHub actually makes pull requests available as an unlisted part of the original repository under refs/pull/$PR/head and refs/pull/$PR/merge, which allows a ma

GitHub actually makes pull requests available as an unlisted part of the original repository under refs/pull/$PR/head and refs/pull/$PR/merge, which allows a malicious author to add themselves to your index, without your involvement. Not to say that this attack is in any way practical, yet. Just that some providers don't require active involvement to try and attempt it.