How to programmatically check the “Password must meet complexity requirements” group policy setting?

Question

Window has five group policy settings related to password security:

• Enforce password history
• Maximum password age
• Minimum password age
• Minimum password length
• Password must meet complexity requirements
• Store passwords using reversible encryption

I know how to use NetUserModalsGet to read most of these items . But it doesn't support checking if password complexity requirement is enabled:

• Enforce password history : usrmod0_password_hist_len
• Maximum password age : usrmod0_max_passwd_age
• Minimum password age : usrmod0_min_passwd_age
• Minimum password length : usrmod0_min_passwd_len
• Password must meet complexity requirements : ?
• Store passwords using reversible encryption :

I also know that WMI's RSOP ( "Resultant set of policy" ) is unsuitable, as it only works on a domain . And i'm certainly not going to crawling through an undocumented binary blob (ie i want the supported way).

Note : I don't care about the "Store passwords using reversible encryption" group policy setting.

Bonus

You can also use the NetUserModalsGet API to retrieve the Account Lockout Policy settings:

• Account lockout duration : usrmod3_lockout_duration
• Account lockout threshold : usrmod3_lockout_threshold
• Reset account lockout counter after : usrmod3_lockout_observation_window

Thus rounding out all the password related group policy options; except for "must meet complexity requirements" .

For completeness, assume a non-domain joined machine (ie no AD server to query, no RSOP to query, etc).

Answer 1

This is accessible using SAM ( Security Account Manager ) APIs.

This API (served by SAMLIB.DLL) is not directly documented (no header, no SDK), but the "protocol" to use it is documented here: [MS-SAMR]: Security Account Manager (SAM) Remote Protocol (Client-to-Server) , you "just" have to remove the r in described SamrXXXX methods.

The ones in question here are SamQueryInformationDomain (and associated SamSetInformationDomain) which will get you a DOMAIN_PASSWORD_INFORMATION structure

typedef struct _DOMAIN_PASSWORD_INFORMATION {
   unsigned short MinPasswordLength;
   unsigned short PasswordHistoryLength;
   unsigned long PasswordProperties;
   OLD_LARGE_INTEGER MaxPasswordAge;
   OLD_LARGE_INTEGER MinPasswordAge;
 } DOMAIN_PASSWORD_INFORMATION,

The PasswordProperties member can contain DOMAIN_PASSWORD_COMPLEX flag:

DOMAIN_PASSWORD_COMPLEX
0x00000001
The server enforces password complexity policy. See section 3.1.1.7.2 for details of the password policy. 

I've provided some C# samples to check this.

First one dumps the policy for all domains served by the current machine's SAM server:

        using (SamServer server = new SamServer(null, SamServer.SERVER_ACCESS_MASK.SAM_SERVER_ENUMERATE_DOMAINS | SamServer.SERVER_ACCESS_MASK.SAM_SERVER_LOOKUP_DOMAIN))
        {
            foreach (string domain in server.EnumerateDomains())
            {
                Console.WriteLine("domain: " + domain);

                var sid = server.GetDomainSid(domain);
                Console.WriteLine(" sid: " + sid);

                var pi = server.GetDomainPasswordInformation(sid);
                Console.WriteLine(" MaxPasswordAge: " + pi.MaxPasswordAge);
                Console.WriteLine(" MinPasswordAge: " + pi.MinPasswordAge);
                Console.WriteLine(" MinPasswordLength: " + pi.MinPasswordLength);
                Console.WriteLine(" PasswordHistoryLength: " + pi.PasswordHistoryLength);
                Console.WriteLine(" PasswordProperties: " + pi.PasswordProperties);
            }
        }

Second one reads and updates the policy for the current machine's domain:

        using (SamServer server = new SamServer(null, SamServer.SERVER_ACCESS_MASK.SAM_SERVER_ALL_ACCESS))
        {
            var sid = server.GetDomainSid(Environment.MachineName);
            var pi = server.GetDomainPasswordInformation(sid);

            // remove password complexity
            pi.PasswordProperties &= ~SamServer.PASSWORD_PROPERTIES.DOMAIN_PASSWORD_COMPLEX;
            server.SetDomainPasswordInformation(sid, pi);
        }

This is the SamServer utility:

public sealed class SamServer : IDisposable
{
    private IntPtr _handle;

    public SamServer(string name, SERVER_ACCESS_MASK access)
    {
        Name = name;
        Check(SamConnect(new UNICODE_STRING(name), out _handle, access, IntPtr.Zero));
    }

    public string Name { get; }

    public void Dispose()
    {
        if (_handle != IntPtr.Zero)
        {
            SamCloseHandle(_handle);
            _handle = IntPtr.Zero;
        }
    }

    public void SetDomainPasswordInformation(SecurityIdentifier domainSid, DOMAIN_PASSWORD_INFORMATION passwordInformation)
    {
        if (domainSid == null)
            throw new ArgumentNullException(nameof(domainSid));

        var sid = new byte[domainSid.BinaryLength];
        domainSid.GetBinaryForm(sid, 0);

        Check(SamOpenDomain(_handle, DOMAIN_ACCESS_MASK.DOMAIN_WRITE_PASSWORD_PARAMS, sid, out IntPtr domain));
        IntPtr info = Marshal.AllocHGlobal(Marshal.SizeOf(passwordInformation));
        Marshal.StructureToPtr(passwordInformation, info, false);
        try
        {
            Check(SamSetInformationDomain(domain, DOMAIN_INFORMATION_CLASS.DomainPasswordInformation, info));
        }
        finally
        {
            Marshal.FreeHGlobal(info);
            SamCloseHandle(domain);
        }
    }

    public DOMAIN_PASSWORD_INFORMATION GetDomainPasswordInformation(SecurityIdentifier domainSid)
    {
        if (domainSid == null)
            throw new ArgumentNullException(nameof(domainSid));

        var sid = new byte[domainSid.BinaryLength];
        domainSid.GetBinaryForm(sid, 0);

        Check(SamOpenDomain(_handle, DOMAIN_ACCESS_MASK.DOMAIN_READ_PASSWORD_PARAMETERS, sid, out IntPtr domain));
        var info = IntPtr.Zero;
        try
        {
            Check(SamQueryInformationDomain(domain, DOMAIN_INFORMATION_CLASS.DomainPasswordInformation, out info));
            return (DOMAIN_PASSWORD_INFORMATION)Marshal.PtrToStructure(info, typeof(DOMAIN_PASSWORD_INFORMATION));
        }
        finally
        {
            SamFreeMemory(info);
            SamCloseHandle(domain);
        }
    }

    public SecurityIdentifier GetDomainSid(string domain)
    {
        if (domain == null)
            throw new ArgumentNullException(nameof(domain));

        Check(SamLookupDomainInSamServer(_handle, new UNICODE_STRING(domain), out IntPtr sid));
        return new SecurityIdentifier(sid);
    }

    public IEnumerable<string> EnumerateDomains()
    {
        int cookie = 0;
        while (true)
        {
            var status = SamEnumerateDomainsInSamServer(_handle, ref cookie, out IntPtr info, 1, out int count);
            if (status != NTSTATUS.STATUS_SUCCESS && status != NTSTATUS.STATUS_MORE_ENTRIES)
                Check(status);

            if (count == 0)
                break;

            var us = (UNICODE_STRING)Marshal.PtrToStructure(info + IntPtr.Size, typeof(UNICODE_STRING));
            SamFreeMemory(info);
            yield return us.ToString();
            us.Buffer = IntPtr.Zero; // we don't own this one
        }
    }

    private enum DOMAIN_INFORMATION_CLASS
    {
        DomainPasswordInformation = 1,
    }

    [Flags]
    public enum PASSWORD_PROPERTIES
    {
        DOMAIN_PASSWORD_COMPLEX = 0x00000001,
        DOMAIN_PASSWORD_NO_ANON_CHANGE = 0x00000002,
        DOMAIN_PASSWORD_NO_CLEAR_CHANGE = 0x00000004,
        DOMAIN_LOCKOUT_ADMINS = 0x00000008,
        DOMAIN_PASSWORD_STORE_CLEARTEXT = 0x00000010,
        DOMAIN_REFUSE_PASSWORD_CHANGE = 0x00000020,
    }

    [Flags]
    private enum DOMAIN_ACCESS_MASK
    {
        DOMAIN_READ_PASSWORD_PARAMETERS = 0x00000001,
        DOMAIN_WRITE_PASSWORD_PARAMS = 0x00000002,
        DOMAIN_READ_OTHER_PARAMETERS = 0x00000004,
        DOMAIN_WRITE_OTHER_PARAMETERS = 0x00000008,
        DOMAIN_CREATE_USER = 0x00000010,
        DOMAIN_CREATE_GROUP = 0x00000020,
        DOMAIN_CREATE_ALIAS = 0x00000040,
        DOMAIN_GET_ALIAS_MEMBERSHIP = 0x00000080,
        DOMAIN_LIST_ACCOUNTS = 0x00000100,
        DOMAIN_LOOKUP = 0x00000200,
        DOMAIN_ADMINISTER_SERVER = 0x00000400,
        DOMAIN_ALL_ACCESS = 0x000F07FF,
        DOMAIN_READ = 0x00020084,
        DOMAIN_WRITE = 0x0002047A,
        DOMAIN_EXECUTE = 0x00020301
    }

    [Flags]
    public enum SERVER_ACCESS_MASK
    {
        SAM_SERVER_CONNECT = 0x00000001,
        SAM_SERVER_SHUTDOWN = 0x00000002,
        SAM_SERVER_INITIALIZE = 0x00000004,
        SAM_SERVER_CREATE_DOMAIN = 0x00000008,
        SAM_SERVER_ENUMERATE_DOMAINS = 0x00000010,
        SAM_SERVER_LOOKUP_DOMAIN = 0x00000020,
        SAM_SERVER_ALL_ACCESS = 0x000F003F,
        SAM_SERVER_READ = 0x00020010,
        SAM_SERVER_WRITE = 0x0002000E,
        SAM_SERVER_EXECUTE = 0x00020021
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct DOMAIN_PASSWORD_INFORMATION
    {
        public short MinPasswordLength;
        public short PasswordHistoryLength;
        public PASSWORD_PROPERTIES PasswordProperties;
        private long _maxPasswordAge;
        private long _minPasswordAge;

        public TimeSpan MaxPasswordAge
        {
            get
            {
                return -new TimeSpan(_maxPasswordAge);
            }
            set
            {
                _maxPasswordAge = value.Ticks;
            }
        }

        public TimeSpan MinPasswordAge
        {
            get
            {
                return -new TimeSpan(_minPasswordAge);
            }
            set
            {
                _minPasswordAge = value.Ticks;
            }
        }
    }

    [StructLayout(LayoutKind.Sequential)]
    private class UNICODE_STRING : IDisposable
    {
        public ushort Length;
        public ushort MaximumLength;
        public IntPtr Buffer;

        public UNICODE_STRING()
            : this(null)
        {
        }

        public UNICODE_STRING(string s)
        {
            if (s != null)
            {
                Length = (ushort)(s.Length * 2);
                MaximumLength = (ushort)(Length + 2);
                Buffer = Marshal.StringToHGlobalUni(s);
            }
        }

        public override string ToString() => Buffer != IntPtr.Zero ? Marshal.PtrToStringUni(Buffer) : null;

        protected virtual void Dispose(bool disposing)
        {
            if (Buffer != IntPtr.Zero)
            {
                Marshal.FreeHGlobal(Buffer);
                Buffer = IntPtr.Zero;
            }
        }

        ~UNICODE_STRING() => Dispose(false);

        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }
    }

    private static void Check(NTSTATUS err)
    {
        if (err == NTSTATUS.STATUS_SUCCESS)
            return;

        throw new Win32Exception("Error " + err + " (0x" + ((int)err).ToString("X8") + ")");
    }

    private enum NTSTATUS
    {
        STATUS_SUCCESS = 0x0,
        STATUS_MORE_ENTRIES = 0x105,
        STATUS_INVALID_HANDLE = unchecked((int)0xC0000008),
        STATUS_INVALID_PARAMETER = unchecked((int)0xC000000D),
        STATUS_ACCESS_DENIED = unchecked((int)0xC0000022),
        STATUS_OBJECT_TYPE_MISMATCH = unchecked((int)0xC0000024),
        STATUS_NO_SUCH_DOMAIN = unchecked((int)0xC00000DF),
    }

    [DllImport("samlib.dll", CharSet = CharSet.Unicode)]
    private static extern NTSTATUS SamConnect(UNICODE_STRING ServerName, out IntPtr ServerHandle, SERVER_ACCESS_MASK DesiredAccess, IntPtr ObjectAttributes);

    [DllImport("samlib.dll", CharSet = CharSet.Unicode)]
    private static extern NTSTATUS SamCloseHandle(IntPtr ServerHandle);

    [DllImport("samlib.dll", CharSet = CharSet.Unicode)]
    private static extern NTSTATUS SamFreeMemory(IntPtr Handle);

    [DllImport("samlib.dll", CharSet = CharSet.Unicode)]
    private static extern NTSTATUS SamOpenDomain(IntPtr ServerHandle, DOMAIN_ACCESS_MASK DesiredAccess, byte[] DomainId, out IntPtr DomainHandle);

    [DllImport("samlib.dll", CharSet = CharSet.Unicode)]
    private static extern NTSTATUS SamLookupDomainInSamServer(IntPtr ServerHandle, UNICODE_STRING name, out IntPtr DomainId);

    [DllImport("samlib.dll", CharSet = CharSet.Unicode)]
    private static extern NTSTATUS SamQueryInformationDomain(IntPtr DomainHandle, DOMAIN_INFORMATION_CLASS DomainInformationClass, out IntPtr Buffer);

    [DllImport("samlib.dll", CharSet = CharSet.Unicode)]
    private static extern NTSTATUS SamSetInformationDomain(IntPtr DomainHandle, DOMAIN_INFORMATION_CLASS DomainInformationClass, IntPtr Buffer);

    [DllImport("samlib.dll", CharSet = CharSet.Unicode)]
    private static extern NTSTATUS SamEnumerateDomainsInSamServer(IntPtr ServerHandle, ref int EnumerationContext, out IntPtr EnumerationBuffer, int PreferedMaximumLength, out int CountReturned);
}