how to secure CMAN against CVE-2012-1675 - or an easier method than ASO

In the Oracle DBA World at the moment CVE-2012-1675 is a great issue. Oracle announced some methods how to secure existing systems. But these are sometimes not that easy, and there is no backport for older systems.
As I investigated the problem how to secure a connection manager I was hinted at Note:1455068.1.
The solution is somewhat easy: Only allow incoming connections to your systems. e.g.
    (rule=(src=*)(dst=10.220.8.114)(srv=*)(act=accept))

In a well designed environment where you can separate your DB Servers from others at low network layers, a set of CMAN might be enough to secure your DBs against CVE-2012-1675.
At least it might be a simple and fast solution to secure your systens from untrusted areas, until you know how to secure the DB servers themselves. Especially for legacy systems it might be the only solution to secure it.