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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/*
* Generate and check the UserChoice Hash, which protects file and protocol
* associations on Windows 10.
*
* NOTE: This is also used in the WDBA, so it avoids XUL and XPCOM.
*
* References:
* - PS-SFTA by Danysys <https://github.com/DanysysTeam/PS-SFTA>
* - based on a PureBasic version by LMongrain
* - AssocHashGen by "halfmeasuresdisabled", see bug 1225660 and
* - SetUserFTA changelog
*/
#include <windows.h>
#include <sddl.h> // for ConvertSidToStringSidW
#include <wincrypt.h> // for CryptoAPI base64
#include <bcrypt.h> // for CNG MD5
#include <winternl.h> // for NT_SUCCESS()
#include "mozilla/ArrayUtils.h"
#include "mozilla/UniquePtr.h"
#include "nsWindowsHelpers.h"
#include "WindowsUserChoice.h"
using namespace mozilla;
UniquePtr<wchar_t[]> GetCurrentUserStringSid() {
HANDLE rawProcessToken;
if (!::OpenProcessToken(::GetCurrentProcess(), TOKEN_QUERY,
&rawProcessToken)) {
return nullptr;
}
nsAutoHandle processToken(rawProcessToken);
DWORD userSize = 0;
if (!(!::GetTokenInformation(processToken.get(), TokenUser, nullptr, 0,
&userSize) &&
GetLastError() == ERROR_INSUFFICIENT_BUFFER)) {
return nullptr;
}
auto userBytes = MakeUnique<unsigned char[]>(userSize);
if (!::GetTokenInformation(processToken.get(), TokenUser, userBytes.get(),
userSize, &userSize)) {
return nullptr;
}
wchar_t* rawSid = nullptr;
if (!::ConvertSidToStringSidW(
reinterpret_cast<PTOKEN_USER>(userBytes.get())->User.Sid, &rawSid)) {
return nullptr;
}
UniquePtr<wchar_t, LocalFreeDeleter> sid(rawSid);
// Copy instead of passing UniquePtr<wchar_t, LocalFreeDeleter> back to
// the caller.
int sidLen = ::lstrlenW(sid.get()) + 1;
auto outSid = MakeUnique<wchar_t[]>(sidLen);
memcpy(outSid.get(), sid.get(), sidLen * sizeof(wchar_t));
return outSid;
}
/*
* Create the string which becomes the input to the UserChoice hash.
*
* @see GenerateUserChoiceHash() for parameters.
*
* @return The formatted string, nullptr on failure.
*
* NOTE: This uses the format as of Windows 10 20H2 (latest as of this writing),
* used at least since 1803.
* There was at least one older version, not currently supported: On Win10 RTM
* (build 10240, aka 1507) the hash function is the same, but the timestamp and
* User Experience string aren't included; instead (for protocols) the string
* ends with the exe path. The changelog of SetUserFTA suggests the algorithm
* changed in 1703, so there may be two versions: before 1703, and 1703 to now.
*/
static UniquePtr<wchar_t[]> FormatUserChoiceString(const wchar_t* aExt,
const wchar_t* aUserSid,
const wchar_t* aProgId,
SYSTEMTIME aTimestamp) {
aTimestamp.wSecond = 0;
aTimestamp.wMilliseconds = 0;
FILETIME fileTime = {0};
if (!::SystemTimeToFileTime(&aTimestamp, &fileTime)) {
return nullptr;
}
// This string is built into Windows as part of the UserChoice hash algorithm.
// It might vary across Windows SKUs (e.g. Windows 10 vs. Windows Server), or
// across builds of the same SKU, but this is the only currently known
// version. There isn't any known way of deriving it, so we assume this
// constant value. If we are wrong, we will not be able to generate correct
// UserChoice hashes.
const wchar_t* userExperience =
L"User Choice set via Windows User Experience "
L"{D18B6DD5-6124-4341-9318-804003BAFA0B}";
const wchar_t* userChoiceFmt =
L"%s%s%s"
L"%08lx"
L"%08lx"
L"%s";
int userChoiceLen = _scwprintf(userChoiceFmt, aExt, aUserSid, aProgId,
fileTime.dwHighDateTime,
fileTime.dwLowDateTime, userExperience);
userChoiceLen += 1; // _scwprintf does not include the terminator
auto userChoice = MakeUnique<wchar_t[]>(userChoiceLen);
_snwprintf_s(userChoice.get(), userChoiceLen, _TRUNCATE, userChoiceFmt, aExt,
aUserSid, aProgId, fileTime.dwHighDateTime,
fileTime.dwLowDateTime, userExperience);
::CharLowerW(userChoice.get());
return userChoice;
}
// @return The MD5 hash of the input, nullptr on failure.
static UniquePtr<DWORD[]> CNG_MD5(const unsigned char* bytes, ULONG bytesLen) {
constexpr ULONG MD5_BYTES = 16;
constexpr ULONG MD5_DWORDS = MD5_BYTES / sizeof(DWORD);
UniquePtr<DWORD[]> hash;
BCRYPT_ALG_HANDLE hAlg = nullptr;
if (NT_SUCCESS(::BCryptOpenAlgorithmProvider(&hAlg, BCRYPT_MD5_ALGORITHM,
nullptr, 0))) {
BCRYPT_HASH_HANDLE hHash = nullptr;
// As of Windows 7 the hash handle will manage its own object buffer when
// pbHashObject is nullptr and cbHashObject is 0.
if (NT_SUCCESS(
::BCryptCreateHash(hAlg, &hHash, nullptr, 0, nullptr, 0, 0))) {
// BCryptHashData promises not to modify pbInput.
if (NT_SUCCESS(::BCryptHashData(hHash, const_cast<unsigned char*>(bytes),
bytesLen, 0))) {
hash = MakeUnique<DWORD[]>(MD5_DWORDS);
if (!NT_SUCCESS(::BCryptFinishHash(
hHash, reinterpret_cast<unsigned char*>(hash.get()),
MD5_DWORDS * sizeof(DWORD), 0))) {
hash.reset();
}
}
::BCryptDestroyHash(hHash);
}
::BCryptCloseAlgorithmProvider(hAlg, 0);
}
return hash;
}
// @return The input bytes encoded as base64, nullptr on failure.
static UniquePtr<wchar_t[]> CryptoAPI_Base64Encode(const unsigned char* bytes,
DWORD bytesLen) {
DWORD base64Len = 0;
if (!::CryptBinaryToStringW(bytes, bytesLen,
CRYPT_STRING_BASE64 | CRYPT_STRING_NOCRLF,
nullptr, &base64Len)) {
return nullptr;
}
auto base64 = MakeUnique<wchar_t[]>(base64Len);
if (!::CryptBinaryToStringW(bytes, bytesLen,
CRYPT_STRING_BASE64 | CRYPT_STRING_NOCRLF,
base64.get(), &base64Len)) {
return nullptr;
}
return base64;
}
static inline DWORD WordSwap(DWORD v) { return (v >> 16) | (v << 16); }
/*
* Generate the UserChoice Hash.
*
* This implementation is based on the references listed above.
* It is organized to show the logic as clearly as possible, but at some
* point the reasoning is just "this is how it works".
*
* @param inputString A null-terminated string to hash.
*
* @return The base64-encoded hash, or nullptr on failure.
*/
static UniquePtr<wchar_t[]> HashString(const wchar_t* inputString) {
auto inputBytes = reinterpret_cast<const unsigned char*>(inputString);
int inputByteCount = (::lstrlenW(inputString) + 1) * sizeof(wchar_t);
constexpr size_t DWORDS_PER_BLOCK = 2;
constexpr size_t BLOCK_SIZE = sizeof(DWORD) * DWORDS_PER_BLOCK;
// Incomplete blocks are ignored.
int blockCount = inputByteCount / BLOCK_SIZE;
if (blockCount == 0) {
return nullptr;
}
// Compute an MD5 hash. md5[0] and md5[1] will be used as constant multipliers
// in the scramble below.
auto md5 = CNG_MD5(inputBytes, inputByteCount);
if (!md5) {
return nullptr;
}
// The following loop effectively computes two checksums, scrambled like a
// hash after every DWORD is added.
// Constant multipliers for the scramble, one set for each DWORD in a block.
const DWORD C0s[DWORDS_PER_BLOCK][5] = {
{md5[0] | 1, 0xCF98B111uL, 0x87085B9FuL, 0x12CEB96DuL, 0x257E1D83uL},
{md5[1] | 1, 0xA27416F5uL, 0xD38396FFuL, 0x7C932B89uL, 0xBFA49F69uL}};
const DWORD C1s[DWORDS_PER_BLOCK][5] = {
{md5[0] | 1, 0xEF0569FBuL, 0x689B6B9FuL, 0x79F8A395uL, 0xC3EFEA97uL},
{md5[1] | 1, 0xC31713DBuL, 0xDDCD1F0FuL, 0x59C3AF2DuL, 0x35BD1EC9uL}};
// The checksums.
DWORD h0 = 0;
DWORD h1 = 0;
// Accumulated total of the checksum after each DWORD.
DWORD h0Acc = 0;
DWORD h1Acc = 0;
for (int i = 0; i < blockCount; ++i) {
for (int j = 0; j < DWORDS_PER_BLOCK; ++j) {
const DWORD* C0 = C0s[j];
const DWORD* C1 = C1s[j];
DWORD input;
memcpy(&input, &inputBytes[(i * DWORDS_PER_BLOCK + j) * sizeof(DWORD)],
sizeof(DWORD));
h0 += input;
// Scramble 0
h0 *= C0[0];
h0 = WordSwap(h0) * C0[1];
h0 = WordSwap(h0) * C0[2];
h0 = WordSwap(h0) * C0[3];
h0 = WordSwap(h0) * C0[4];
h0Acc += h0;
h1 += input;
// Scramble 1
h1 = WordSwap(h1) * C1[1] + h1 * C1[0];
h1 = (h1 >> 16) * C1[2] + h1 * C1[3];
h1 = WordSwap(h1) * C1[4] + h1;
h1Acc += h1;
}
}
DWORD hash[2] = {h0 ^ h1, h0Acc ^ h1Acc};
return CryptoAPI_Base64Encode(reinterpret_cast<const unsigned char*>(hash),
sizeof(hash));
}
UniquePtr<wchar_t[]> GetAssociationKeyPath(const wchar_t* aExt) {
const wchar_t* keyPathFmt;
if (aExt[0] == L'.') {
keyPathFmt =
L"SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Explorer\\FileExts\\%s";
} else {
keyPathFmt =
L"SOFTWARE\\Microsoft\\Windows\\Shell\\Associations\\"
L"UrlAssociations\\%s";
}
int keyPathLen = _scwprintf(keyPathFmt, aExt);
keyPathLen += 1; // _scwprintf does not include the terminator
auto keyPath = MakeUnique<wchar_t[]>(keyPathLen);
_snwprintf_s(keyPath.get(), keyPathLen, _TRUNCATE, keyPathFmt, aExt);
return keyPath;
}
UniquePtr<wchar_t[]> GenerateUserChoiceHash(const wchar_t* aExt,
const wchar_t* aUserSid,
const wchar_t* aProgId,
SYSTEMTIME aTimestamp) {
auto userChoice = FormatUserChoiceString(aExt, aUserSid, aProgId, aTimestamp);
if (!userChoice) {
return nullptr;
}
return HashString(userChoice.get());
}
/*
* NOTE: The passed-in current user SID is used here, instead of getting the SID
* for the owner of the key. We are assuming that this key in HKCU is owned by
* the current user, since we want to replace that key ourselves. If the key is
* owned by someone else, then this check will fail; this is ok because we would
* likely not want to replace that other user's key anyway.
*/
CheckUserChoiceHashResult CheckUserChoiceHash(const wchar_t* aExt,
const wchar_t* aUserSid) {
auto keyPath = GetAssociationKeyPath(aExt);
if (!keyPath) {
return CheckUserChoiceHashResult::ERR_OTHER;
}
HKEY rawAssocKey;
if (::RegOpenKeyExW(HKEY_CURRENT_USER, keyPath.get(), 0, KEY_READ,
&rawAssocKey) != ERROR_SUCCESS) {
return CheckUserChoiceHashResult::ERR_OTHER;
}
nsAutoRegKey assocKey(rawAssocKey);
FILETIME lastWriteFileTime;
{
HKEY rawUserChoiceKey;
if (::RegOpenKeyExW(assocKey.get(), L"UserChoice", 0, KEY_READ,
&rawUserChoiceKey) != ERROR_SUCCESS) {
return CheckUserChoiceHashResult::ERR_OTHER;
}
nsAutoRegKey userChoiceKey(rawUserChoiceKey);
if (::RegQueryInfoKeyW(userChoiceKey.get(), nullptr, nullptr, nullptr,
nullptr, nullptr, nullptr, nullptr, nullptr, nullptr,
nullptr, &lastWriteFileTime) != ERROR_SUCCESS) {
return CheckUserChoiceHashResult::ERR_OTHER;
}
}
SYSTEMTIME lastWriteSystemTime;
if (!::FileTimeToSystemTime(&lastWriteFileTime, &lastWriteSystemTime)) {
return CheckUserChoiceHashResult::ERR_OTHER;
}
// Read ProgId
DWORD dataSizeBytes = 0;
if (::RegGetValueW(assocKey.get(), L"UserChoice", L"ProgId", RRF_RT_REG_SZ,
nullptr, nullptr, &dataSizeBytes) != ERROR_SUCCESS) {
return CheckUserChoiceHashResult::ERR_OTHER;
}
// +1 in case dataSizeBytes was odd, +1 to ensure termination
DWORD dataSizeChars = (dataSizeBytes / sizeof(wchar_t)) + 2;
UniquePtr<wchar_t[]> progId(new wchar_t[dataSizeChars]());
if (::RegGetValueW(assocKey.get(), L"UserChoice", L"ProgId", RRF_RT_REG_SZ,
nullptr, progId.get(), &dataSizeBytes) != ERROR_SUCCESS) {
return CheckUserChoiceHashResult::ERR_OTHER;
}
// Read Hash
dataSizeBytes = 0;
if (::RegGetValueW(assocKey.get(), L"UserChoice", L"Hash", RRF_RT_REG_SZ,
nullptr, nullptr, &dataSizeBytes) != ERROR_SUCCESS) {
return CheckUserChoiceHashResult::ERR_OTHER;
}
dataSizeChars = (dataSizeBytes / sizeof(wchar_t)) + 2;
UniquePtr<wchar_t[]> storedHash(new wchar_t[dataSizeChars]());
if (::RegGetValueW(assocKey.get(), L"UserChoice", L"Hash", RRF_RT_REG_SZ,
nullptr, storedHash.get(),
&dataSizeBytes) != ERROR_SUCCESS) {
return CheckUserChoiceHashResult::ERR_OTHER;
}
auto computedHash =
GenerateUserChoiceHash(aExt, aUserSid, progId.get(), lastWriteSystemTime);
if (!computedHash) {
return CheckUserChoiceHashResult::ERR_OTHER;
}
if (::CompareStringOrdinal(computedHash.get(), -1, storedHash.get(), -1,
FALSE) != CSTR_EQUAL) {
return CheckUserChoiceHashResult::ERR_MISMATCH;
}
return CheckUserChoiceHashResult::OK_V1;
}
bool CheckBrowserUserChoiceHashes() {
auto userSid = GetCurrentUserStringSid();
if (!userSid) {
return false;
}
const wchar_t* exts[] = {L"https", L"http", L".html", L".htm"};
for (int i = 0; i < ArrayLength(exts); ++i) {
switch (CheckUserChoiceHash(exts[i], userSid.get())) {
case CheckUserChoiceHashResult::OK_V1:
break;
case CheckUserChoiceHashResult::ERR_MISMATCH:
case CheckUserChoiceHashResult::ERR_OTHER:
return false;
}
}
return true;
}
UniquePtr<wchar_t[]> FormatProgID(const wchar_t* aProgIDBase,
const wchar_t* aAumi) {
const wchar_t* progIDFmt = L"%s-%s";
int progIDLen = _scwprintf(progIDFmt, aProgIDBase, aAumi);
progIDLen += 1; // _scwprintf does not include the terminator
auto progID = MakeUnique<wchar_t[]>(progIDLen);
_snwprintf_s(progID.get(), progIDLen, _TRUNCATE, progIDFmt, aProgIDBase,
aAumi);
return progID;
}
bool CheckProgIDExists(const wchar_t* aProgID) {
HKEY key;
if (::RegOpenKeyExW(HKEY_CLASSES_ROOT, aProgID, 0, KEY_READ, &key) !=
ERROR_SUCCESS) {
return false;
}
::RegCloseKey(key);
return true;
}