GitHub Branch Source Plugin connects to a user-specified GitHub API URL (e.g. GitHub Enterprise) as part of form validation and completion (e.g. to verify Scan Credentials are correct). This functionality improperly checked permissions, allowing any user with Overall/Read access to Jenkins to connect to any web server and send credentials with a known ID, thereby possibly capturing them. Additionally, this functionality did not require POST requests be used, thereby allowing the above to be performed without direct access to Jenkins via Cross-Site Request Forgery. An enumeration of credentials IDs in this plugin now requires the permission to have Extended Read permission (when that permission is enabled; otherwise Configure permission) to the job in whose context credentials are being accessed. If no job context exists, Overall/Administer permission is required.
