Since at least v3.4, the OpenShift documentation  has specified the format for corsAllowedOrigins to accurately match intended hostnames. Since at least v3.7, installs will default to use the correct regular expression formatted variables. Earlier versions may be configured with plain strings, a configuration which will persist across cluster upgrades, opening them to cross origin vulnerabilities such as this.
At a minimum, you should ensure that the corsAllowedOrigin definition within master-config.yaml contains elements in the form
corsAllowedOrigins: - (?i)//my\.subdomain\.domain\.com(:|\z)
and not the form
corsAllowedOrigins: - domain.com
as the first will permit cross origin requests only if the host matches exactly, whereas the second will permit from any host that merely contains the string (such as ABCDdomain.com or even domain.comABCD.com).