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:ryany@pantek.com] Sent: Thursday, May 08, 2003 6:28 PM
To: at4r@3wdesign.es
Cc: vuln-dev@securityfocus.com

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.

Do you need help?

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Thanks,
Ryan Yagatich

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>This bug allow a malicious an attacker to execute data with privileges of a

>user that is browsing the hard disk with explorer.
<snip>
>
> strcpy(path,"\\aT4r[at]3WDesign.es Security");

> bof=fopen(path,"w");
<snip> Received on Fri May 9 12:56:34 2003