An issue was discovered in HttpKernel in Symfony 2.7.0 through 2.7.48, 2.8.0 through 2.8.43, 3.3.0 through 3.3.17, 3.4.0 through 3.4.13, 4.0.0 through 4.0.13, and 4.1.0 through 4.1.2. When using HttpCache, the values of the X-Forwarded-Host headers are implicitly set as trusted while this should be forbidden, leading to potential host header injection.