The function CryptProtectMemory allows an application to encrypt memory for one of three scenarios, process, logon session and computer. When using the logon session option (CRYPTPROTECTMEMORY_SAME_LOGON flag) the encryption key is generated based on the logon session identifier, this is for sharing memory between processes running within the same logon. As this might also be used for sending data from one process to another it supports extracting the logon session id from the impersonation token. The issue is the implementation in CNG.sys doesn't check the impersonation level of the token when capturing the logon session id (using SeQueryAuthenticationIdToken) so a normal user can impersonate at Identification level and decrypt or encrypt data for that logon session. This might be an issue if there's a service which is vulnerable to a named pipe planting attack or is storing encrypted data in a world readable shared memory section. This is the proof of concept code that demonstrates the issue. This affects Windows 7, 8.1 Update 32/64 bit.
http://dl.packetstormsecurity.net/1501-exploits/Poc_CNGLogonSessionImpersonation.zip
