A denial of service vulnerability exists when SymCrypt improperly handles a specially crafted digital signature.An attacker could exploit the vulnerability by creating a specially crafted connection or message.The security update addresses the vulnerability by correcting the way SymCrypt handles digital signatures., aka 'SymCrypt Denial of Service Vulnerability'.
https://www.tenable.com/blog/microsoft-s-july-2019-patch-tuesday-what-you-need-to-know
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2019-0865