Orbit Downloader "Download failed" buffer overflow
Core Security Technologies - CoreLabs Advisory
Title: Orbit Downloader "Download failed" buffer overflow
Advisory ID: CORE-2008-0314
Advisory URL: http://www.coresecurity.com/?action=item&id=2211
Date published: 2008-04-03
Date of last update: 2008-04-03
Vendors contacted: Orbit Downloader team
Release mode: Coordinated release
Orbit downloader  is vulnerable to a buffer overflow attack, which can be exploited by malicious remote attackers to execute arbitrary code. The vulnerability is due to Orbit not properly converting an URL ascii string to unicode. This can be exploited to execute arbitrary code by downloading a file from a specially crafted URL.
Update to Orbit downloader 2.6.5, available at <http://dl.orbitdownloader.com/dl/OrbitDownloaderSetup.exe>, or visit the vendor homepage at <http://www.orbitdownloader.com>.
This vulnerability was discovered and researched by Diego Juarez from Core Security Technologies.
When Orbit is unable to download a file, a balloon control is popped in the notification area. This is the code that takes care of drawing text to said control:
.text:004A56D0 sub_4A56D0 proc near ; CODE XREF: sub_42AAC0+321 p .text:004A56D0 ; sub_439610+321 p ... .text:004A56D0 .text:004A56D0 String = word ptr -2000h .text:004A56D0 hDC = dword ptr 4 .text:004A56D0 arg_4 = dword ptr 8 .text:004A56D0 lpRect = dword ptr 0Ch .text:004A56D0 uFormat = dword ptr 10h .text:004A56D0 .text:004A56D0 mov eax, 2000h ; reserve 0x2000 (8192) bytes in the stack .text:004A56D5 call __alloca_probe .text:004A56DA push edi .text:004A56DB mov ecx, 800h .text:004A56E0 xor eax, eax .text:004A56E2 lea edi, [esp+2004h+String] .text:004A56E6 rep stosd .text:004A56E8 mov eax, [esp+2004h+arg_4] .text:004A56EF pop edi .text:004A56F0 mov ecx, [eax+8] .text:004A56F3 mov eax, [eax+4] .text:004A56F6 test eax, eax .text:004A56F8 jnz short loc_4A56FF .text:004A56FA mov eax, ds:?_C@?1??_Nullstr@? [basic_string@DU](<mailto:basic_string@DU>)? char_traits@[D@std](<mailto:D@std>)@@V? allocator@D@2@@std@@CAPBDXZ@4DB ; .text:004A56FF .text:004A56FF loc_4A56FF: ; CODE XREF: sub_4A56D0+28 j .text:004A56FF lea edx, [esp+2000h+String] .text:004A5703 push 2000h ; cchWideChar (write up to 16384 bytes to the buffer) .text:004A5708 push edx ; lpWideCharStr .text:004A5709 push ecx ; cchMultiByte .text:004A570A push eax ; lpMultiByteStr .text:004A570B push 0 ; dwFlags .text:004A570D push 0 ; CodePage .text:004A570F call ds:MultiByteToWideChar .text:004A5715 mov ecx, [esp+2000h+uFormat] .text:004A571C mov edx, [esp+2000h+lpRect] .text:004A5723 push ecx ; uFormat .text:004A5724 mov ecx, [esp+2004h+hDC] .text:004A572B push edx ; lpRect .text:004A572C push eax ; nCount .text:004A572D lea eax, [esp+200Ch+String] .text:004A5731 push eax ; lpString .text:004A5732 push ecx ; hDC .text:004A5733 call ds:DrawTextW .text:004A5739 add esp, 2000h .text:004A573F retn .text:004A573F endp ;sub_4A56D0
According to MSDN , the Win32 API function
int MultiByteToWideChar( UINT CodePage, DWORD dwFlags, LPCSTR lpMultiByteStr, int cbMultiByte, LPWSTR lpWideCharStr, int cchWideChar );
has a parameter
cchWideChar which should be the "size, in WCHAR values, of the buffer indicated by lpWideCharStr". By supplying a download URL longer than 4096 bytes, if the download fails,
MultiByteToWideChar will overflow the 8192 bytes buffer in the stack and write up to 0x2000 WCHARs (16384 bytes) to it, overwriting internal structures and enabling arbitrary code execution.
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