An old issue since the seventies of the last century
when I am asked to execute an order, I have to limit myself to orders given by those who I trust or have to trust (instructors, some [computer] programs, I myself?). Never I may follow those who want me to commit a crime ;->
A software system run under and exposing a certain identity may only trust its own components (libs, taks etc...) or components from other identies the executing identity trusts.
Commonly a software system only needs its own libraries (and subtasks) and those offered by the identity "system". Why should an unidentified component be trusted?
Micorosft itself has built up a whole PKI and forces vendors to sign their components digitally just to avoid execution of untrusted components. Microsoft statement,“Hence, this issue cannot directly be addressed in Windows without breaking expected functionality. Instead, it requires developers to ensure they code secure library loads.", foils the security policy of Microsoft itself.
Evolving dangers by executing untrusted components have been known since the early sixties of the last century, IBM and BULL published basic results around 1966....Some of these results founded the security design of the AS/400 under OS/400.
RBAC/MAC forces a linking policy for processes / tasks run under certain and/or predefined identities. Given this failure Microsoft can not obey basic requirements to fulfill higher protection profiles.
Solaris 10 never allows linking of untrusted libraries against setuid programs or programs executed under uid 0, see http://docs.sun.com/app/docs/doc/816-5165/ld.so.1-1?l=all&a=view, keyword "security".
In summary Microsoft did not learn its lessons from the last half century, and even foils its own security policies --- once again an epic fail.