An improper access control vulnerability was identified in GitHub Enterprise Server that allowed users with access to any repository to retrieve limited code content from another repository by creating a diff between the repositories. To exploit this vulnerability, an attacker needed to know the name of a private repository along with its branches, tags, or commit SHAs that they could use to trigger compare/diff functionality and retrieve limited code without proper authorization. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.18, and was fixed in versions 3.14.17, 3.15.12, 3.16.8 and 3.17.5. This vulnerability was reported via the GitHub Bug Bounty program.
The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.