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gretty

Edit/Delete Protected Registry Key Value

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My question: Is it possible to edit a registry key's value when it was created using a custom security descriptor? Do I need to call RegSetKeyValueEx with a SECURITY_ATTRIBUTES structure? If not, then I would need to delete the key then recreate it.

I am attempting to edit(or delete then rewrite) a registry key value but its not working. Some important information is that I created the registry key with a custom Security Descriptor. The custom security descriptor only has the KEY_READ Registry Key Security and Access Rights set.

But I cant even delete the key because of its ACL security descriptor. This is a problem because when I uninstall I wont even be able to delete the registry key then either. The reason why I create the registry key with a custom security descriptor is so the user cant change it accidentally or on purpose. The key tells me if my application has run before.

Does anyone know how I can edit/delete a registry key of this type?

My code(that attempts to edit my key and shows how I created the key in the first place): 

    // Code to change key value
    LONG lResult = RegOpenKeyEx(HKEY_CURRENT_USER, _T("Software/MyApplication"), 0, KEY_READ, &hKey);
    LONG setValueRes = RegSetValueEx(hKey, _T("FirstRunSignafier"), 0, REG_DWORD, (LPBYTE) &firstRunSignafierValue,
                                     (DWORD) sizeof(firstRunSignafierValue));
    // Error Value of setValueRes is 5. lResult succeeds

    
    // Code that creates the registry key
    int  recordFirstApplicationRun()
    {
        tstring REG_FIRST_RUN_SIGNIFIER = _T("Software\\MyApplication");
        HKEY hKey;
        LONG lResult;
        int      res                      = 1;
        DWORD dwValue, dwType, dwSize = sizeof(dwValue);
        DWORD firstRunSignafierValue  = 1;
        DWORD keyAlreadyExists;    // Two potential values: REG_CREATED_NEW_KEY or REG_OPENED_EXISTING_KEY
        PSID pEveryoneSID              = NULL;
        PACL pACL                      = NULL;
        PSECURITY_DESCRIPTOR pSD      = NULL;
        SECURITY_ATTRIBUTES secAttr;
    
        createSecurityAttributes(&secAttr, pEveryoneSID, pACL, pSD);
        LONG createRes = RegCreateKeyEx(HKEY_CURRENT_USER, &REG_FIRST_RUN_SIGNIFIER[0], 0, NULL, REG_OPTION_NON_VOLATILE,
                                        KEY_WRITE|KEY_WRITE, &secAttr, &hKey, &keyAlreadyExists);
        if (createRes != ERROR_SUCCESS) {
            //_tprintf(_T("Failed to create key: Last Error: %x, Return Val: %x\n"), GetLastError(), createRes);
            CPP_Utilities::outputLastError("Failed to create key");
            res = -1;
            goto Cleanup;
        }
    
        //CPP_Utilities::outputLastErrorEx( (keyAlreadyExists == REG_CREATED_NEW_KEY) ? _T("Created new registry key"):_T("Registry key already exists") );
        _tprintf( (keyAlreadyExists == REG_CREATED_NEW_KEY) ? _T("Created new registry key\n"):_T("Registry key already exists\n") );
    
        // To Write a DWORD to the registry
        LONG setValueRes = RegSetValueEx(hKey, _T("FirstRunSignafier"), 0, REG_DWORD, (LPBYTE) &firstRunSignafierValue,
                                         (DWORD) sizeof(firstRunSignafierValue));
        if (setValueRes != ERROR_SUCCESS) {
            _tprintf(_T("B: %X\n"), setValueRes);
            CPP_Utilities::outputLastError("Failed to set registry value");
            res = -2;
            goto Cleanup;
        }
    
        Cleanup:
            if (pEveryoneSID)
                FreeSid(pEveryoneSID);
            if (pACL)
                LocalFree(pACL);
            if (pSD)
                LocalFree(pSD);
            if (hKey)
                RegCloseKey(hKey);
    
        return res;
    }
    
    int createSecurityAttributes(SECURITY_ATTRIBUTES* secAttr, PSID pEveryoneSID, PACL pACL, PSECURITY_DESCRIPTOR pSD)
    {
        // Pre:    Memory release for parameters MUST be handled by caller
    
        EXPLICIT_ACCESS ea;
        DWORD dwRes;
        /*PSID*/ pEveryoneSID                    = NULL;
        /*PACL*/ pACL                            = NULL;
        /*PSECURITY_DESCRIPTOR*/ pSD            = NULL;
        SID_IDENTIFIER_AUTHORITY SIDAuthWorld    = SECURITY_WORLD_SID_AUTHORITY;
    
        // Create a well-known SID for the Everyone group.
        if(!AllocateAndInitializeSid(&SIDAuthWorld, 1, SECURITY_WORLD_RID, 0, 0, 0, 0, 0, 0, 0, &pEveryoneSID)) {
            _tprintf(_T("AllocateAndInitializeSid Error %u\n"), GetLastError());
            CPP_Utilities::outputLastError("AllocateAndInitializeSid Error");
            return -1;
        }
    
        // Initialize an EXPLICIT_ACCESS structure for an ACE. The ACE will allow Everyone read access to the key.
        ZeroMemory(&ea, sizeof(EXPLICIT_ACCESS));
        ea.grfAccessPermissions = KEY_READ;
        ea.grfAccessMode        = SET_ACCESS;
        ea.grfInheritance        = NO_INHERITANCE;
        ea.Trustee.TrusteeForm    = TRUSTEE_IS_SID;
        ea.Trustee.TrusteeType    = TRUSTEE_IS_WELL_KNOWN_GROUP;
        ea.Trustee.ptstrName    = (LPTSTR) pEveryoneSID;
    
        // Create a new ACL that contains the new ACEs.
        dwRes = SetEntriesInAcl(1, &ea, NULL, &pACL);
        if (ERROR_SUCCESS != dwRes) {
            _tprintf(_T("SetEntriesInAcl Error %u\n"), GetLastError());
            CPP_Utilities::outputLastError("SetEntriesInAcl Error");
            return -2;
        }
    
        // Initialize a security descriptor.  
        pSD = (PSECURITY_DESCRIPTOR) LocalAlloc(LPTR, SECURITY_DESCRIPTOR_MIN_LENGTH);
        if (NULL == pSD) {
            _tprintf(_T("LocalAlloc Error %u\n"), GetLastError());
            CPP_Utilities::outputLastError("LocalAlloc Error");
            return -3;
        }
     
        if (!InitializeSecurityDescriptor(pSD, SECURITY_DESCRIPTOR_REVISION)) {  
            _tprintf(_T("InitializeSecurityDescriptor Error %u\n"), GetLastError());
            CPP_Utilities::outputLastError("InitializeSecurityDescriptor Error");
            return -4;
        }
     
        // Add the ACL to the security descriptor.
        if (!SetSecurityDescriptorDacl(pSD, TRUE, pACL, FALSE)) {  
            _tprintf(_T("SetSecurityDescriptorDacl Error %u\n"), GetLastError());
            CPP_Utilities::outputLastError("SetSecurityDescriptorDacl Error");
            return -5;
        }
    
        // Initialize a security attributes structure.
        secAttr->nLength                = sizeof (SECURITY_ATTRIBUTES);
        secAttr->lpSecurityDescriptor    = pSD;
        secAttr->bInheritHandle            = FALSE;
    
        return 1;
    }
 
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The documentation you linked to describes exactly how to solve this. Enable the correct privileges and take ownership of the key, then modify it to your desires.

 

(Note that in general a user with sufficient rights can do the exact same thing, so don't rely too much on your notion that nobody will edit or modify the key!)

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