Windows process with Untrusted Integrity level - windows

Question

I couldn't find much information about Untrusted integrity level in Windows, and have some questions about it:
Is there a place where an untrusted integrity level process can create named objects? (mutexes, events, etc..)
Should untrusted integrity level process be able to open an existing named object, that was given a security descriptor in it's creation time with ACE with SYSTEM_MANDATORY_LABEL_NO_WRITE_UP to MandatoryLevelUntrusted? When I try it, it fails with 0xc0000022(access denied), while with MandatoryLevelLow it works great.
How do usually untrusted integrity processes communicate with their broker process? (like how does a google chrome tab communicates with the google chrome broker?)

Answer 1

Is there a place where an untrusted integrity level process can create
named objects? (mutexes, events, etc..)
by default - no. code with untrusted token (thread or process) can create object only in directory with Untrusted Mandatory Level - no one standard folders have this kind of label. some have Low Mandatory Level but untrusted - no.
but you can easy create this folder yourself. with Untrusted Mandatory Level and NULL DACL - untrusted code can create objects in this folder.
NTSTATUS CreateUntrustedFolder(PHANDLE phObject, PCUNICODE_STRING ObjectName)
{
ULONG cb = MAX_SID_SIZE;
PSID UntrustedSid = (PSID)alloca(MAX_SID_SIZE);
if (CreateWellKnownSid(WinUntrustedLabelSid, 0, UntrustedSid, &cb))
{
PACL Sacl = (PACL)alloca(cb += sizeof(ACL) + sizeof(ACE_HEADER) + sizeof(ACCESS_MASK));
InitializeAcl(Sacl, cb, ACL_REVISION);
if (AddMandatoryAce(Sacl, ACL_REVISION, 0, 0, UntrustedSid))
{
SECURITY_DESCRIPTOR sd;
InitializeSecurityDescriptor(&sd, SECURITY_DESCRIPTOR_REVISION);
SetSecurityDescriptorDacl(&sd, TRUE, NULL, FALSE);
SetSecurityDescriptorSacl(&sd, TRUE, Sacl, FALSE);
OBJECT_ATTRIBUTES oa = { sizeof(oa), 0, (PUNICODE_STRING)ObjectName, OBJ_CASE_INSENSITIVE|OBJ_OPENIF, &sd };
return ZwCreateDirectoryObject(phObject, DIRECTORY_ALL_ACCESS, &oa);
}
}
return STATUS_UNSUCCESSFUL;
}
about untrusted code creation - if start process at begin with token marked as untrusted integrity level - process fail to start. this when ntdll.dll try load kernel32.dll - it try open section \KnownDlls\kernel32.dll with SECTION_MAP_WRITE as well , but this object have Low Mandatory Level with SYSTEM_MANDATORY_LABEL_NO_WRITE_UP - as result untrusted code fail open this section with write access.
as result you need initially create process say with Low Mandatory Level and then set untrusted level
ULONG SetProcessUntrusted(HANDLE hProcess)
{
TOKEN_MANDATORY_LABEL tml = { { (PSID)alloca(MAX_SID_SIZE), SE_GROUP_INTEGRITY } };
ULONG cb = MAX_SID_SIZE;
HANDLE hToken;
if (!CreateWellKnownSid(WinUntrustedLabelSid, 0, tml.Label.Sid, &cb) ||
!OpenProcessToken(hProcess, TOKEN_ADJUST_DEFAULT, &hToken))
{
return GetLastError();
}
ULONG dwError = NOERROR;
if (!SetTokenInformation(hToken, TokenIntegrityLevel, &tml, sizeof(tml)))
{
dwError = GetLastError();
}
CloseHandle(hToken);
return dwError;
}
Should untrusted integrity level process be able to open an existing
named object
this depend from object label(level and mask) , code intergrity level and required access. if code intergrity level >= object label level - we can open object (if dacl let do this). otherwise need look for object label mask and required access. for example object have Low Mandatory Level with SYSTEM_MANDATORY_LABEL_NO_WRITE_UP and code Untrusted Mandatory Level - this code can open object with read and execute access, but fail open it for write access