A denial of service vulnerability exists in Skype for Business, aka 'Skype for Business and Lync Server Denial of Service Vulnerability'.

A denial of service vulnerability exists in Skype for Business. An attacker who successfully exploited the vulnerability could cause Skype for Business to stop responding. Note that the denial of service would not allow an attacker to execute code or to elevate the attacker's user rights.
To exploit the vulnerability, an attacker needs to obtain a dial-in link for a vulnerable server and then initiates a series of calls within a short amount of time.
The update addresses the vulnerability by correcting the way that Skype for Business server handles objects in memory.

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2019-1029

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2019-1029

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2019-1029 Types: Patch, Vendor Advisory