Argument injection in the download commit resource through the at parameter - CVE-2017-18087

The download commit resource in Atlassian Bitbucket Server from version 5.1.0 before version 5.1.7, from version 5.2.0 before version 5.2.5, from version 5.3.0 before version 5.3.3 and from version 5.4.0 before version 5.4.1 allows remote attackers to write files to disk potentially allowing them to gain code execution, exploit CVE-2017-1000117 if a vulnerable version of git is in use, and or determine if an internal service exists via an argument injection vulnerability in the at parameter.