An information disclosure vulnerability exists in SymCrypt during the OAEP decryption stage. An attacker who successfully exploited this vulnerability could obtain information to further compromise the user’s system. To exploit this vulnerability, an attacker would have to log on to an affected system and run a specially crafted application. The vulnerability would not allow an attacker to execute code or to elevate user rights directly, but it could be used to obtain information that could be used to try to further compromise the affected system. The update addresses the vulnerability through a software change to the OAEP decoding operations.
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2019-1171