Inshell Security Advisory
http://www.inshell.net


1. ADVISORY INFORMATION
-----------------------
Product:        WinAmp
Vendor URL:     www.winamp.com
Type:           Stack-based Buffer Overflow [CWE-121]
Date found:     2013-06-05
Date published: 2013-07-01
CVSSv2 Score:   Bug #1: 7,5 (AV:N/AC:L/Au:N/C:P/I:P/A:P)
    Bug #2: 3,7 (AV:L/AC:H/Au:N/C:P/I:P/A:P)
CVE:            CVE-2013-4694


2. CREDITS
----------
These vulnerabilities were discovered and researched by Julien Ahrens
from Inshell Security.


3. VERSIONS AFFECTED
--------------------
WinAmp v5.63, older versions may be affected too.


4. VULNERABILITY DESCRIPTION (BUG #1)
-------------------------------------
The application loads the directories in %PROGRAMFILES%\WinAmp\Skins on
startup to determine the skins that have been installed and to list them
in the application menu point "Skins" and in the Skins Browser. But the
application does not properly validate the length of the directory name
before passing it as argument to a lstrcpynW call in the library
gen_jumpex.dll, which leads to a buffer overflow condition with possible
code execution.

This flaw is also exploitable via the %APPDATA%\WinAmp\winamp.ini. The
application loads the contents on startup, but does not properly
validate the length of the string loaded from the "skin" key before
passing it as an argument to the same lstrcpynW call in the library
gen_jumpex.dll, which leads to the same buffer overflow condition.

An attacker either needs to trick the victim to download and apply an
arbitrary skin package in order to exploit the vulnerability or to copy
an arbitrary winamp.ini into the %APPDATA%\WinAmp directory. Successful
exploits can allow attackers to execute arbitrary code with the
privileges of the user running the application. Failed exploits will
result in a denial-of-service condition.


4. VULNERABILITY DESCRIPTION (BUG #2)
-------------------------------------
The application loads the string of the GUI "Search" field from the
"WinAmp Library" when entered by a user and after switching to another
menu point, but does not properly validate the length of the string
before passing it as an argument to a GetDlgItemTextW call in the
library ml_local.dll, which leads to a buffer overflow condition with
possible code execution.

An attacker needs local access to the client in order to exploit the
vulnerability. Successful exploits can allow attackers to execute
arbitrary code with the privileges of the user running the application.
Failed exploits will result in a denial-of-service condition.


5. PROOF-OF-CONCEPT (DEBUG) (Bug #1)
------------------------------------
Registers:
EAX 3B3C08EB
ECX 7C80BAFC kernel32.7C80BAFC
EDX 00430010 winamp.00430010
EBX 0000007E
ESP 00C1F290 UNICODE "CCCCCCCCCCCCCCCCCCCCCCCCCCCC"
EBP 00430043 winamp.00430043
ESI 001961E8
EDI 0000060B
EIP 00430060 winamp.00430060
C 0  ES 0023 32bit 0(FFFFFFFF)
P 1  CS 001B 32bit 0(FFFFFFFF)
A 0  SS 0023 32bit 0(FFFFFFFF)
Z 1  DS 0023 32bit 0(FFFFFFFF)
S 0  FS 003B 32bit 7FFDE000(FFF)
T 0  GS 0000 NULL
D 0
O 0  LastErr ERROR_INVALID_WINDOW_HANDLE (00000578)
EFL 00010246 (NO,NB,E,BE,NS,PE,GE,LE)
ST0 empty +NaN
ST1 empty
ST2 empty
ST3 empty
ST4 empty
ST5 empty
ST6 empty
ST7 empty
               3 2 1 0      E S P U O Z D I
FST 0120  Cond 0 0 0 1  Err 0 0 1 0 0 0 0 0  (LT)
FCW 027F  Prec NEAR,53  Mask    1 1 1 1 1 1

Stackview:
ESP-20   > 00430043  CC  winamp.00430043
ESP-1C   > 0043004B  KC  winamp.0043004B
ESP-18   > 7C80BAFC      kernel32.7C80BAFC
ESP-14   > 00430043  CC  winamp.00430043
ESP-10   > 00430043  CC  winamp.00430043
ESP-C    > 00430043  CC  winamp.00430043
ESP-8    > 00430043  CC  winamp.00430043
ESP-4    > 00430043  CC  winamp.00430043
ESP ==>  > 00430043  CC  winamp.00430043
ESP+4    > 00430043  CC  winamp.00430043
ESP+8    > 00430043  CC  winamp.00430043
ESP+C    > 00430043  CC  winamp.00430043
ESP+10   > 00430043  CC  winamp.00430043
ESP+14   > 00430043  CC  winamp.00430043
ESP+18   > 00430043  CC  winamp.00430043
ESP+1C   > 00430043  CC  winamp.00430043
ESP+20   > 00430043  CC  winamp.00430043

Vulnerable code part:
.text:1001A5B8                 push    eax             ; lpString2
.text:1001A5B9                 lea     eax, [ebp+String1]
.text:1001A5BF                 push    eax             ; lpString1
.text:1001A5C0                 call    ds:lstrcpynW
.text:1001A5C6                 cmp     word ptr [ebp+wParam], si
.text:1001A5CD                 jnz     short loc_1001A5E2
.text:1001A5CF                 mov     dword_100310B4, 1
.text:1001A5D9                 cmp     [ebp+String1], si
.text:1001A5E0                 jz      short loc_1001A5E8
.text:1001A5E2
.text:1001A5E2 loc_1001A5E2:                           ; CODE XREF:
sub_1001A551+7Cj
.text:1001A5E2                 mov     dword_100310B4, esi
.text:1001A5E8
.text:1001A5E8 loc_1001A5E8:                           ; CODE XREF:
sub_1001A551+8Fj
.text:1001A5E8                 pop     esi
.text:1001A5E9                 leave
.text:1001A5EA                 retn
.text:1001A5EA sub_1001A551    endp


5. PROOF-OF-CONCEPT (DEBUG) (Bug #2)
------------------------------------
Registers:
EAX 00000000
ECX 079A9D68 ml_local.079A9D68
EDX 00380608
EBX 00000000
ESP 00C1E46C UNICODE "CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC"
EBP 00430043 winamp.00430043
ESI 00000000
EDI 00000000
EIP 00430043 winamp.00430043
C 0  ES 0023 32bit 0(FFFFFFFF)
P 1  CS 001B 32bit 0(FFFFFFFF)
A 0  SS 0023 32bit 0(FFFFFFFF)
Z 1  DS 0023 32bit 0(FFFFFFFF)
S 0  FS 003B 32bit 7FFDE000(FFF)
T 0  GS 0000 NULL
D 0
O 0  LastErr ERROR_INVALID_WINDOW_HANDLE (00000578)
EFL 00010246 (NO,NB,E,BE,NS,PE,GE,LE)
ST0 empty
ST1 empty
ST2 empty
ST3 empty
ST4 empty
ST5 empty
ST6 empty
ST7 empty
               3 2 1 0      E S P U O Z D I
FST 0000  Cond 0 0 0 0  Err 0 0 0 0 0 0 0 0  (GT)
FCW 027F  Prec NEAR,53  Mask    1 1 1 1 1 1

Stackview:
ESP-20   > 00430043  CC  winamp.00430043
ESP-1C   > 00430043  CC  winamp.00430043
ESP-18   > 00430043  CC  winamp.00430043
ESP-14   > 00430043  CC  winamp.00430043
ESP-10   > 00430043  CC  winamp.00430043
ESP-C    > 00430043  CC  winamp.00430043
ESP-8    > 00430043  CC  winamp.00430043
ESP-4    > 00430043  CC  winamp.00430043
ESP ==>  > 00430043  CC  winamp.00430043
ESP+4    > 00430043  CC  winamp.00430043
ESP+8    > 00430043  CC  winamp.00430043
ESP+C    > 00430043  CC  winamp.00430043
ESP+10   > 00430043  CC  winamp.00430043
ESP+14   > 00430043  CC  winamp.00430043
ESP+18   > 00430043  CC  winamp.00430043
ESP+1C   > 00430043  CC  winamp.00430043
ESP+20   > 00430043  CC  winamp.00430043

Vulnerable code part:
.text:07990871                 lea     eax, [ebp+WideCharStr]
.text:07990877                 push    eax             ; lpString
.text:07990878                 push    3EEh            ; nIDDlgItem
.text:0799087D                 push    [ebp+hDlg]      ; hDlg
.text:07990880                 call    ds:GetDlgItemTextW
.text:07990886                 lea     eax, [ebp+WideCharStr]
[...]
.text:0799097C                 mov     dword_79A9D68, eax
.text:07990981                 mov     dword_79A9D70, eax
.text:07990986                 mov     dword_79A9D6C, eax
.text:0799098B                 mov     dword_79ACB54, eax
.text:07990990                 pop     ebx
.text:07990991                 leave
.text:07990992                 retn


6. SOLUTION
-----------
Update to latest version v5.64 or newer.


7. REPORT TIMELINE
------------------
2013-06-05: Discovery of the vulnerability
2013-06-06: Vendor acknowledgement of the issue
2013-06-11: Vendor already fixed this issue in v5.7 Beta build 3403
2013-06-12: Confirmation that the issue is fixed
2013-06-19: Vendor releases v5.64 which includes the fix
2013-07-01: Coordinated Disclosure


8. REFERENCES
-------------
http://security.inshell.net
http://forums.winamp.com/showthread.php?t=364291