The signature-update functionality in Windows Defender on Microsoft Windows 7 and Windows Server 2008 R2 relies on an incorrect pathname, which allows local users to gain privileges via a Trojan horse application in the %SYSTEMDRIVE% top-level directory, aka "Microsoft Windows 7 Defender Improper Pathname Vulnerability."
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A17253
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2013/ms13-058