Improper access control in GitHub Enterprise Server leading to the enumeration of private repository names

Summary

An improper access control vulnerability was identified in GitHub Enterprise Server that allowed authenticated users of the instance to determine the names of unauthorized private repositories given their numerical IDs. This vulnerability did not allow unauthorized access to any repository content besides the name. This vulnerability affected all versions of GitHub Enterprise Server prior to 2.22 and was fixed in versions 2.21.6, 2.20.15, and 2.19.21. This vulnerability was reported via the GitHub Bug Bounty program.