On September 5, 2022, we reverted a recent change to our indirect pull request merge logic that was causing some pull requests to be incorrectly marked as merged. This could happen if a pull request's head branch was force pushed and resulted in the pull request showing no new commits compared to the base branch. The original change went live on August 1, 2022 and caused confusion about why some pull requests were marked as merged by a contributor who did not have the necessary permissions. It also had the side effect of removing the "first time contributor" flag from these contributors without them having made an accepted contribution by the repository maintainers. Depending on repository settings, this could have allowed first time contributors to run GitHub Actions workflows based on their branches.
At no point were users able to push changes or merge pull requests in repositories to which they did not have appropriate authorization. After the change was reverted, GitHub conducted an investigation into any bypasses of the "first time contributor" flag and found no evidence of abuse.