Atlassian Bitbucket Server before 4.7.1 allows remote attackers to read the first line of an arbitrary file via a directory traversal attack on the pull requests resource.
https://jira.atlassian.com/browse/BSERV-8819
https://confluence.atlassian.com/bitbucketserver/bitbucket-server-4-7-release-notes-829052416.html