A Code Injection vulnerability was identified in GitHub Enterprise Server that allowed attackers to inject malicious code into the query selector via the identity property in the message handling function. This enabled the exfiltration of sensitive data by manipulating the DOM, including authentication tokens. To execute the attack, the victim must be logged into GitHub and interact with the attacker controlled malicious webpage containing the hidden iframe. This vulnerability occurs due to an improper sequence of validation, where the origin check occurs after accepting the user-controlled identity property. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.11.16, 3.12.10, 3.13.5, 3.14.2, and 3.15.0. This vulnerability was reported via the GitHub Bug Bounty program.