Attempt to reset a FWP Engine Security Descriptor.

fwpacl.c

#include <stdio.h>
#include <windows.h>
#include <fwpmu.h>
#include <sddl.h>
#include <malloc.h>


//
// Attempt to reset a FWP Engine Security Descriptor.
// For https://github.com/henrypp/simplewall/issues/680
//
//  Tavis Ormandy -- taviso@gmail.com
//

#pragma comment(lib, "FWPUCLNT")
#pragma comment(lib, "ADVAPI32")

char DefaultSecurityInfo[] =
    "O:LS"  // Owner: Local service
    "G:LS"  // Group: Local service
    "D:AI"  // Dacl: (Auto Inherited)

    // Builtin Administrators
    "(A;;0xf07ff;;;BA)"
    "(A;OICIIO;GA;;;BA)"

    // Network configuration operators
    "(A;;0x307ff;;;NO)"
    "(A;OICIIO;GXGWGR;;;NO)"

    // MpsSvc (Malware Protection)
    "(A;;0x307ff;;;S-1-5-80-3088073201-1464728630-1879813800-1107566885-823218052)"
    "(A;OICIIO;GXGWGR;;;S-1-5-80-3088073201-1464728630-1879813800-1107566885-823218052)"

    // NlaSvc (Network Location Awareness)
    "(A;;0x203f4;;;S-1-5-80-3141615172-2057878085-1754447212-2405740020-3916490453)"
    "(A;OICIIO;GXGR;;;S-1-5-80-3141615172-2057878085-1754447212-2405740020-3916490453)"

    // PolicyAgent
    "(A;;0x307ff;;;S-1-5-80-3044542841-3639452079-4096941652-1606687743-1256249853)"
    "(A;OICIIO;GXGWGR;;;S-1-5-80-3044542841-3639452079-4096941652-1606687743-1256249853)"

    // RpcSs
    "(A;;0x307ff;;;S-1-5-80-979556362-403687129-3954533659-2335141334-1547273080)"
    "(A;OICIIO;GXGWGR;;;S-1-5-80-979556362-403687129-3954533659-2335141334-1547273080)"

    // WdiServiceHost
    "(A;;0x203f4;;;S-1-5-80-3139157870-2983391045-3678747466-658725712-1809340420)"
    "(A;OICIIO;GXGR;;;S-1-5-80-3139157870-2983391045-3678747466-658725712-1809340420)"

    // IKE/IpSec
    "(A;;0x307ff;;;S-1-5-80-1510742542-3632397484-604094731-3920060944-1272132581)"
    "(A;OICIIO;GXGWGR;;;S-1-5-80-1510742542-3632397484-604094731-3920060944-1272132581)"

    // Everyone (Write Properties / Delete Subtree)
    "(A;OICI;RPDT;;;WD)";

int main(int argc, char **argv)
{
    HANDLE EngineHandle;
    PSECURITY_DESCRIPTOR EngineOwner;
    LPSTR CurrentSecurityInfo;

    if (FwpmEngineOpen0(NULL,
                        RPC_C_AUTHN_DEFAULT,
                        NULL,
                        NULL,
                        &EngineHandle) != ERROR_SUCCESS) {
        fprintf(stderr, "FwpmEngineOpen0 failed, %#X\n", GetLastError());
        return 1;
    }

    if (FwpmEngineGetSecurityInfo0(EngineHandle,
                                   OWNER_SECURITY_INFORMATION
                                 | GROUP_SECURITY_INFORMATION
                                 | DACL_SECURITY_INFORMATION,
                                   NULL,
                                   NULL,
                                   NULL,
                                   NULL,
                                   &EngineOwner) != ERROR_SUCCESS) {
        fprintf(stderr, "FwpmEngineGetSecurityInfo0 Failed, %#x\n", GetLastError());
        return 1;
    }

    if (ConvertSecurityDescriptorToStringSecurityDescriptorA(EngineOwner,
                                                             SDDL_REVISION_1,
                                                             OWNER_SECURITY_INFORMATION
                                                           | GROUP_SECURITY_INFORMATION
                                                           | SACL_SECURITY_INFORMATION
                                                           | DACL_SECURITY_INFORMATION,
                                                             &CurrentSecurityInfo,
                                                             NULL) == FALSE) {
        fprintf(stderr, "Failed to parse descriptor %#x\n", GetLastError());
        return 1;
    }

    fprintf(stderr, "Filter Engine Security Descriptor: %s\n", CurrentSecurityInfo);

    if (strcmp(CurrentSecurityInfo, DefaultSecurityInfo) != 0) {
        fprintf(stderr, "*** WARNING ***\n");
        fprintf(stderr, "This is not the default BFE security descrptor.\n");
        fprintf(stderr, "Would you like me to restore the default? y/n  ");
        fflush(stderr);

        if (_getch() == 'y') {
            PSECURITY_DESCRIPTOR AbsSecurityDescriptor;
            PSECURITY_DESCRIPTOR RelSecurityDescriptor;
            PACL pDacl, pSacl;
            PSID pOwner, pGroup;
            DWORD DaclSize, SaclSize;
            DWORD OwnerSize, GroupSize;
            DWORD AbsSecurityDescriptorSize;
            PSID DefaultSid;

            fputc('\n', stderr);

            if (ConvertStringSecurityDescriptorToSecurityDescriptorA(DefaultSecurityInfo,
                                                                     SDDL_REVISION_1,
                                                                     &RelSecurityDescriptor,
                                                                     NULL) == FALSE) {
                fprintf(stderr, "Sorry, failed to convert descritpor\n");
                fprintf(stderr, "No changes were made.\n");
                return 1;
            }

            // Now we have to make it an absolute descriptor so that we can get
            // the component pointers.
            MakeAbsoluteSD(RelSecurityDescriptor,
                           NULL,
                           &AbsSecurityDescriptorSize,
                           NULL,
                           &DaclSize,
                           NULL,
                           &SaclSize,
                           NULL,
                           &OwnerSize,
                           NULL,
                           &GroupSize);

            if (GetLastError() != ERROR_INSUFFICIENT_BUFFER) {
                fprintf(stderr, "Unexpected Result from MakeAbsoluteSD()\n");
                return 1;
            }

            // Allocate the requested sizes.
            AbsSecurityDescriptor = _malloca(AbsSecurityDescriptorSize);
            pDacl  = _malloca(DaclSize);
            pSacl  = _malloca(SaclSize);
            pOwner = _malloca(OwnerSize);
            pGroup = _malloca(GroupSize);

            if (!MakeAbsoluteSD(RelSecurityDescriptor,
                                AbsSecurityDescriptor,
                                &AbsSecurityDescriptorSize,
                                pDacl,
                                &DaclSize,
                                pSacl,
                                &SaclSize,
                                pOwner,
                                &OwnerSize,
                                pGroup,
                                &GroupSize)) {
                fprintf(stderr, "MakeAbsoluteSD failed to parse descriptor\n");
                return 1;
            }

            DWORD Result;
            Result = FwpmEngineSetSecurityInfo0(EngineHandle,
                                                GROUP_SECURITY_INFORMATION
                                              | DACL_SECURITY_INFORMATION,
                                                pOwner,
                                                pGroup,
                                                pDacl,
                                                pSacl);

            if (Result != ERROR_SUCCESS) {
                fprintf(stderr, "Sorry, failed to reset security descriptor, %#x\n", Result);
                return 1;
            }

            // No need to free the absolute descriptor, it's on the stack.
            LocalFree(RelSecurityDescriptor);
        }
    } else {
        fprintf(stderr,  "OK, that's the default ACL\n");
    }

    fputc('\n', stderr);
    LocalFree(CurrentSecurityInfo);
    FwpmFreeMemory0(&EngineOwner);
    FwpmEngineClose0(EngineHandle);
    return 0;
}