Summary
Repository and organization project boards listed the pull requests that reference each issue on the board without checking whether the viewer can read them. When a private pull request mentions an issue on a board the viewer can open, the board revealed the private repository's path and the pull request's number, title and state, to anonymous visitors in the case of a public board. The pull request body, diff and files were not exposed. Boards now skip linked pull requests in repositories where the viewer cannot read pull requests.