Improper control flow in GitHub Enterprise Server hosted Pages leads to remote code execution

Summary

A remote code execution vulnerability was identified in GitHub Enterprise Server that could be exploited when building a GitHub Pages site. To exploit this vulnerability, an attacker would need permission to create and build a GitHub Pages site on the GitHub Enterprise Server instance. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.3 and was fixed in versions 3.0.21, 3.1.13, 3.2.5. This vulnerability was reported via the GitHub Bug Bounty program.