An issue was discovered in JetBrains TeamCity 2018.2.4. The TeamCity server was not using some security-related HTTP headers. The issue was fixed in TeamCity 2019.1.
https://euvd.enisa.europa.eu/vulnerability/EUVD-2019-6125
https://blog.jetbrains.com/blog/2019/09/26/jetbrains-security-bulletin-q2-2019/