Samba versions 3.6.3 and all versions previous to this are affected by a vulnerability that allows remote code execution as the "root" user from an anonymous connection. The code generator for Samba's remote procedure call (RPC) code contained an error which caused it to generate code containing a security flaw. This generated code is used in the parts of Samba that control marshalling and unmarshalling of RPC calls over the network. The flaw caused checks on the variable containing the length of an allocated array to be done independently from the checks on the variable used to allocate the memory for that array. As both these variables are controlled by the connecting client it makes it possible for a specially crafted RPC call to cause the server to execute arbitrary code. As this does not require an authenticated connection it is the most serious vulnerability possible in a program, and users and vendors are encouraged to patch their Samba installations immediately.