Description
Drupal Core is prone to a security bypass vulnerability. Exploiting this issue may allow attackers to bypass certain security restrictions and perform otherwise restricted actions. Drupal Core versions 8.x ranging from 8.0.0 and up to and including 8.5.5 are vulnerable.
Remediation
Update to Drupal Core version 8.5.6 or latest
References
https://www.drupal.org/SA-CORE-2018-005
https://symfony.com/blog/cve-2018-14773-remove-support-for-legacy-and-risky-http-headers
https://framework.zend.com/security/advisory/ZF2018-01
https://drupal.stackexchange.com/questions/266784/how-critical-is-sa-core-2018-005