This information came from Marcus Meissner of Suse:

Sebastian Krahmer of SUSE audited Mono and found a tempfile
race condition in the Mono Core libraries, found in
mcs/class/System/System.CodeDom.Compiler/TempFileCollection.cs

The diff (actual there are 2 commits) to fix it are here:
http://svn.myrealbox.com/viewcvs/trunk/mcs/class/System/System.CodeDom.Compiler/TempFileCollection.cs?rev=65441&r1=57836&r2=65441
I have only looked at them briefly, but the fix looks OK.

This can be used by a local attacker for instance with help of
System.Xml.Serialization (SerializationCodeGenerator.cs), which
compiles .cs code into .dlls on the fly, to inject code into a
running Mono process.