Do high-integrity tokens *have* to have the Administrators group enabled?

Question

When UAC is enabled, and you log in with an administrative account, you get two tokens:

• the elevated token; this has the Administrators group enabled, is hi

Answer 1

No, the kernel does not require that the integrity level and elevation type of a token match up with the status of the Administrators group. This means that a process having a high integrity level, or TokenElevationTypeFull, does not necessarily have administrator access.

In particular, note that using runas /trustlevel:0x20000 from an administrative command prompt will result in a process that does not have administrator privilege but nonetheless runs with high integrity and (if UAC is enabled) will have TokenElevationTypeFull. (As discovered here.) I believe this represents a bug in runas.

This sample code demonstrates the behaviour; if run with admin privilege, it launches a subprocess with the administrators group (and all privileges except SeChangeNotifyPrivilege) disabled but which is still running with high integrity and TokenElevationTypeFull.

#include <Windows.h>
#include <Sddl.h>

#include <stdio.h>

PSID admins_sid;

void get_membership(HANDLE token)
{
    BOOL is_enabled;
    HANDLE itoken;

    if (!DuplicateToken(token, SecurityIdentification, &itoken))
    {
        printf("DuplicateToken: %u\n", GetLastError());
        return;
    }

    if (!CheckTokenMembership(itoken, admins_sid, &is_enabled))
    {
        printf("CheckTokenMembership: %u\n", GetLastError());
        CloseHandle(itoken);
        return;
    }

    CloseHandle(itoken);

    printf("Administrators group enabled: %u\n", is_enabled);
    return;
}

void get_integrity(HANDLE token)
{
    char buffer[4096];
    char * stringsid;

    TOKEN_MANDATORY_LABEL *token_mandatory_label = (TOKEN_MANDATORY_LABEL *)buffer;
    DWORD dw;

    if (!GetTokenInformation(token, TokenIntegrityLevel, buffer, sizeof(buffer), &dw))
    {
        printf("GetTokenInformation: %u\n", GetLastError());
        return;
    }

    if (!ConvertSidToStringSidA(token_mandatory_label->Label.Sid, &stringsid))
    {
        printf("ConvertSidToStringSid: %u\n", GetLastError());
        return;
    }

    printf("SID: %s\n", stringsid);
}

void get_elevation(HANDLE token)
{
    TOKEN_ELEVATION_TYPE elevation;
    DWORD dw;

    if (!GetTokenInformation(token, 
        TokenElevationType, &elevation, sizeof(elevation), &dw))
    {
        printf("GetTokenInformation: %u\n", GetLastError());
        return;
    }

    printf("Elevation type : %u\n", (DWORD)elevation);
}   

void test(void)
{
    HANDLE token1, token2;
    SID_AND_ATTRIBUTES sids_to_disable;
    STARTUPINFOA si = {sizeof(STARTUPINFOA)};
    PROCESS_INFORMATION pi;

    if (!OpenProcessToken(GetCurrentProcess(), MAXIMUM_ALLOWED, &token1))
    {
        printf("OpenProcessToken: %u\n", GetLastError());
        return;
    }

    printf("token1:\n");
    get_membership(token1);
    get_integrity(token1);
    get_elevation(token1);

    sids_to_disable.Attributes = 0;
    sids_to_disable.Sid = admins_sid;

    if (!CreateRestrictedToken(token1, 
        DISABLE_MAX_PRIVILEGE, 1, &sids_to_disable, 0, NULL, 0, NULL, &token2))
    {
        printf("CreateRestrictedToken: %u\n", GetLastError());
        return;
    }

    printf("token2:\n");
    get_membership(token2);
    get_integrity(token2);
    get_elevation(token2);

    if (!CreateProcessAsUserA(token2, 
        NULL, "cmd", NULL, NULL, FALSE, CREATE_NEW_CONSOLE, NULL, NULL, &si, &pi))
    {
        printf("CreateProcessAsUser: %u\n", GetLastError());
        return;
    }
}

int main(int argc, char ** argv)
{
    {
        SID_IDENTIFIER_AUTHORITY SIDAuth = SECURITY_NT_AUTHORITY;
        if(! AllocateAndInitializeSid( &SIDAuth, 2,
                         SECURITY_BUILTIN_DOMAIN_RID,
                         DOMAIN_ALIAS_RID_ADMINS,
                         0, 0, 0, 0, 0, 0,
                         &admins_sid) ) 
        {
            printf( "AllocateAndInitializeSid: %u\n", GetLastError());
            return 1;
        }
    }

    test();
    return 0;
}

Output when run from an elevated command prompt:

token1:
Administrators group enabled: 1
SID: S-1-16-12288
Elevation type : 2
token2:
Administrators group enabled: 0
SID: S-1-16-12288
Elevation type : 2

If you run the sample code again from the child process, you can confirm that the child process did retain these properties:

token1:
Administrators group enabled: 0
SID: S-1-16-12288
Elevation type : 2

If UAC is disabled, the elevation type is TokenElevationTypeDefault but otherwise the outcome is the same:

token1:
Administrators group enabled: 1
SID: S-1-16-12288
Elevation type : 1
token2:
Administrators group enabled: 0
SID: S-1-16-12288
Elevation type : 1

As expected, the limited token looks like this:

token1:
Administrators group enabled: 0
SID: S-1-16-8192
Elevation type : 3

Or if you're logged in as a non-admin user, whether UAC is enabled or not:

token1:
Administrators group enabled: 0
SID: S-1-16-8192
Elevation type : 1

(All tests run on Windows 7 SP1 x64.)