Improper authentication vulnerability in GitHub Enterprise Server leading to modification of secret gists

Summary

An improper authentication vulnerability was identified in GitHub Enterprise Server that allowed an unauthorized actor to modify other users' secret gists by authenticating through an SSH certificate authority. To do so, a user had to know the secret gist's URL. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.9 and was fixed in versions 3.4.18, 3.5.15, 3.6.11, 3.7.8, and 3.8.1. This vulnerability was reported via the GitHub Bug Bounty program.