Hi @ll,

versions of Microsoft Security Essentials before the current
v4.2 (see <https://support.microsoft.com/kb/2805304>) have a
vulnerability that could lead to execution of arbitrary code
in the security context of the LocalSystem account (almost like
<https://support.microsoft.com/kb/2781197> alias
<http://technet.microsoft.com/security/bulletin/ms13-034>).

The "UninstallString" written to

[HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Uninstall\Microsoft Security Client]
"UninstallString"="C:\\Program Files\\Microsoft Security Client\\Setup.exe /X"

contains unquoted spaces.
This command may be called by Windows Update Agent or deployment
agents running under the LocalSystem account.


Timeline:
~~~~~~~~~

2012-12-05    vendor informed

2013-12-06    vendor acknowledged report

2013-02-13    vendor released fixed version


Stefan Kanthak