An elevation of privilege vulnerability exists in Windows Installer because of the way Windows Installer handles certain filesystem operations.
To exploit the vulnerability, an attacker would require unprivileged execution on the victim system. After successfully exploiting the vulnerability, an attacker could run arbitrary code with elevated privileges. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.
The security update addresses the vulnerability by correcting the way Windows Installer handles certain filesystem operations.