Internet Explorer漏洞分析(三)[上]——VBScript Scripting Engine初探
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2021-03-08 21:23
Internet Explorer漏洞分析(三)[上]——VBScript Scripting Engine初探
1.本文一共1514个字 28张图 预计阅读时间10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.本篇文章是文章Internet Explorer漏洞分析(三)[下]——CVE-2014-6332的前置知识,对vbscrip.dll组件进行逆向分析,以及VBScript数据类型,数组,VarType函数,LenB函数详细分析,并介绍VBS脚本调试技巧
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
近来分析Internet Explorer历史漏洞,遂对VBScript脚本解析引擎进行研究,具体环境如下:
•OS版本:Windows 7 Service Pack 1•Internet Explorer版本:8.0.7601.17514•vbscript.dll版本:5.8.7601.17514
0x01 变量
VBScript中仅有一种数据类型——Variant。其结构定义如下:
typedef struct tagVARIANT {
union {
struct {
VARTYPE vt;
WORD wReserved1;
WORD wReserved2;
WORD wReserved3;
union {
LONGLONG llVal;
LONG lVal;
BYTE bVal;
SHORT iVal;
FLOAT fltVal;
DOUBLE dblVal;
VARIANT_BOOL boolVal;
VARIANT_BOOL __OBSOLETE__VARIANT_BOOL;
SCODE scode;
CY cyVal;
DATE date;
BSTR bstrVal;
IUnknown *punkVal;
IDispatch *pdispVal;
SAFEARRAY *parray;
BYTE *pbVal;
SHORT *piVal;
LONG *plVal;
LONGLONG *pllVal;
FLOAT *pfltVal;
DOUBLE *pdblVal;
VARIANT_BOOL *pboolVal;
VARIANT_BOOL *__OBSOLETE__VARIANT_PBOOL;
SCODE *pscode;
CY *pcyVal;
DATE *pdate;
BSTR *pbstrVal;
IUnknown **ppunkVal;
IDispatch **ppdispVal;
SAFEARRAY **pparray;
VARIANT *pvarVal;
PVOID byref;
CHAR cVal;
USHORT uiVal;
ULONG ulVal;
ULONGLONG ullVal;
INT intVal;
UINT uintVal;
DECIMAL *pdecVal;
CHAR *pcVal;
USHORT *puiVal;
ULONG *pulVal;
ULONGLONG *pullVal;
INT *pintVal;
UINT *puintVal;
struct {
PVOID pvRecord;
IRecordInfo *pRecInfo;
} __VARIANT_NAME_4;
} __VARIANT_NAME_3;
} __VARIANT_NAME_2;
DECIMAL decVal;
} __VARIANT_NAME_1;
} VARIANT;
其中VARTYPE
可参阅[Microsoft Docs——VARIANT Type Constants]https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-oaut/3fe7db9f-5803-4dc4-9d14-5425d3f5461f。例:
'显式声明
Dim Name,Age,Hex,Pi
Name="Ethon"
Age=27
Hex=&h80000000
Pi=3.1415926
'隐式声明
Hello="ABC123"
赋值对应函数为vbscript!AssignVar
,于该函数处设断,查看其参数:
0x400C
表示VT_VARIANT
:
判断pvargSrc—>vt
值(具体数值可自行分析,不赘述),若均不满足,执行如下语句:
简单来说,即VariantCopyInd(&pvarDest, pvargSrc)
——>copy pvarDest
to pvarg
:
隐式声明变量其pvarg
全为零:
0x02 数组
数组存储结构由SAFEARRAY
定义:
typedef struct tagSAFEARRAY {
USHORT cDims;
USHORT fFeatures;
ULONG cbElements;
ULONG cLocks;
PVOID pvData;
SAFEARRAYBOUND rgsabound[1];
} SAFEARRAY;
其中各字段含义可参阅[Microsoft Docs——SAFEARRAY]https://docs.microsoft.com/en-us/windows/win32/api/oaidl/ns-oaidl-safearray ,SAFEARRAYBOUND
结构定义如下:
typedef struct tagSAFEARRAYBOUND {
ULONG cElements;
LONG lLbound;
} SAFEARRAYBOUND, *LPSAFEARRAYBOUND;
数组定义及赋值操作:
Dim stu_name(3)
stu_name(0)="Alan"
stu_name(1)="Susan"
stu_name(2)="Lisa"
stu_name(3)="Mary"
VBS中数组下标由0开始,数组元素个数为n+1(Dim array_name(n)
)。另一种定义数组方法:
Dim stu_name
stu_name=Array("Alan","Susan","Lisa","Mary")
对应函数为vbscript!MakeArray
:
传递给函数的参数有二——cDims
对应维数,VAR
对应n。cDims
应介于1-64:
先来看一维数组的创建:
为rgsabound
结构各字段赋值:
之后则直接调用SafeArrayCreate
函数进行创建,各参数含义可参阅[Microsoft Docs——SafeArrayCreate]https://docs.microsoft.com/en-us/windows/win32/api/oleauto/nf-oleauto-safearraycreate 。创建完成:
为数组元素赋值则直接将该元素所在内存偏移传递给vbscript!AssignVar
:
下面来看看二维数组(Dim stu_name(2,3)
)创建过程:
可以看到数组各维大小于内存中并列存储,之后调用VAR::PvarGetTypeVal
逐一读取为rgsabound
中cElements
字段赋值:
各维大小于内存中由最高维——>最低维存储,故读取时首先计算出v3
变量指向最低维大小所在内存偏移,之后递减。创建完成:
Redim
语句用于重新定义数组大小:
'定义一维动态数组
Dim MyArray()
'重新定义该数组大小
ReDim MyArray(3)
MyArray(0) = "A"
MyArray(1) = "B"
MyArray(2) = "C"
MyArray(3) = "C"
再次调用vbscript!MakeArray
过程如下:
而在重新定义时加上Preserve
关键字用于保留之前元素:
Dim MyArray()
ReDim MyArray(3)
MyArray(0) = "A"
MyArray(1) = "B"
MyArray(2) = "C"
MyArray(3) = "D"
ReDim Preserve MyArray(5)
MyArray(4) = "E"
MyArray(5) = "F"
其对应vbscript!RedimPreserveArray
函数:
为psaboundNew
各字段赋值完成后传递给SafeArrayRedim
函数:
0x03 可用于调试时函数
IsEmpty(var)
对应vbscript!VbsIsEmpty
,其第三个参数对应var
。一例:
<!doctype html>
<html lang="en">
<head>
</head>
<body>
<script LANGUAGE="VBScript">
dim a
a = &h1234
IsEmpty(a)
</script>
</body>
</html>
IsObject(var)
对应vbscript!VbsIsObject
,同样,其第三个参数对应var
。一例:
<!doctype html>
<html lang="en">
<head>
</head>
<body>
<script LANGUAGE="VBScript">
dim a
a = &h1234
IsObject(a)
</script>
</body>
</html>
在调试时可借助这两个函数以确定变量值或内存位置。
0x04 VarType函数
<!doctype html>
<html lang="en">
<head>
</head>
<body>
<script LANGUAGE="VBScript">
dim a
a = &h1234
VarType(a)
</script>
</body>
</html>
VarType
对应vbscript!VbsVarType
,其调用GetVarType
函数获取类型值并完成赋值操作:
参数1用于存储类型值,参数2为VarType
参数:
GetVarType
函数调用PvarGetVarVal
——判断类型值是否为0x4A
或0x0C
:
之后与0x09
进行比较,若不是则直接返回对象进而获取vt
值:
由VbsVarType
函数完成最终赋值给参数1操作:
0x05 LenB函数
<!doctype html>
<html lang="en">
<head>
</head>
<body>
<script LANGUAGE="VBScript">
On Error Resume Next
Dim length,a
a=1.12345678901235
length=LenB("Hello")
length=LenB(a)
</script>
</body>
</html>
该函数用于返回存储字符串字节大小,其对应vbscript!VbsLenB
。参数为字符串时,该函数先是call VAR::BstrGetVal
,返回pbstrVal
:
之后call cbLengthBstr
返回长度:
参数为变量时, VAR::BstrGetVal
函数调用VAR::PvarConvert
,将其内容转换为字符串:
之后再进行计算:
cbLengthBstr
函数功能仅是读取字符串存储位置之前4字节内容,该内容为字符串长度:
0x06 参阅链接
•[Microsoft Docs——SAFEARRAY structure]https://docs.microsoft.com/en-us/windows/win32/api/oaidl/ns-oaidl-safearray•[Microsoft Docs——VARIANT structure]https://docs.microsoft.com/en-us/windows/win32/api/oaidl/ns-oaidl-variant•[Microsoft Docs——VARIANT Type Constants]https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-oaut/3fe7db9f-5803-4dc4-9d14-5425d3f5461f•[Microsoft Docs——SafeArrayCreate]https://docs.microsoft.com/en-us/windows/win32/api/oleauto/nf-oleauto-safearraycreate•[Microsoft Docs——DECIMAL structure]https://docs.microsoft.com/en-us/windows/win32/api/wtypes/ns-wtypes-decimal-r1