Thursday, February 28, 2008

XMLHTTP, res://, and name look-ups

After reading another one of RSnake's posts about file enumeration using res://, I went back to see how XMLHTTP handles this protocol. It can make for some interesting results if the URI can be controlled by the user.


set http = createobject("Msxml2.XMLHTTP") "GET", "res://cmd.exe"

msxml3.dll error '80070005'
Access is denied.
------------------------------------------------------------ "GET", "res://notepad.exe"

msxml3.dll error '80070715'
The specified resource type cannot be found in the image file.
------------------------------------------------------------ "GET", "res://garbage.exe"

msxml3.dll error '80070002'
The system cannot find the file specified.

------------------------------------------------------------ "GET", "res://shdoclc.dll/IESecHelp.htm"

"Internet Explorer Enhanced Security Configuration places your server and Microsoft Internet Explorer ...."

When a server makes a remote or local request for a user specified resource, there is a lot more going on server-side then you might initially realize. Filemon is a good tool to see what's going when trying to access local files. And of course, Wireshark is fun for seeing what happens when you request remote files.

For example, on a Windows box, specifying http://shortname will cause the server to send out NetBios Name Service (NBNS) UDP broadcasts on its subnet, while requesting will get the server to make DNS requests (assuming the host is not in the DNS cache). Clearly, you can get the server to reach out to more machines than just the server hosting the content you're trying to fetch, which means we have more attack vectors to worry about.

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