经常听说的ASP上传漏洞，即是将一些木马文件修改后缀名（修改为图像文件后缀），进行上传。
针对此情况使用下列函数进行辨别：
<%
'****************************************
'CheckFileType 函数用来检查文件是否为图片文件
'参数filename是本地文件的路径
'如果是文件jpeg,gif,bmp,png图片中的一种，函数返回true，否则返回false
'***********************************
const adTypeBinary=1
dim jpg(1):jpg(0)=CByte(&HFF):jpg(1)=CByte(&HD8)
dim bmp(1):bmp(0)=CByte(&H42):bmp(1)=CByte(&H4D)
dim png(3):png(0)=CByte(&H89):png(1)=CByte(&H50):png(2)=CByte(&H4E):png(3)=CByte(&H47)
dim gif(5):gif(0)=CByte(&H47):gif(1)=CByte(&H49):gif(2)=CByte(&H46):gif(3)=CByte(&H39):gif(4)=CByte(&H38):gif(5)=CByte(&H61)
function CheckFileType(filename)
on error resume next
CheckFileType=false
dim fstream,fileExt,stamp,i
fileExt=mid(filename,InStrRev(filename,".")+1)
set fstream=Server.createobject("ADODB.Stream")
fstream.Open
fstream.Type=adTypeBinary
fstream.LoadFromFile filename
fstream.position=0
select case fileExt
case "jpg","jpeg"
stamp=fstream.read(2)
for i=0 to 1
if ascB(MidB(stamp,i+1,1))=jpg(i) then CheckFileType=true else CheckFileType=false
next
case "gif"
stamp=fstream.read(6)
for i=0 to 5
if ascB(MidB(stamp,i+1,1))=gif(i) then CheckFileType=true else CheckFileType=false
next
case "png"
stamp=fstream.read(4)
for i=0 to 3
if ascB(MidB(stamp,i+1,1))=png(i) then CheckFileType=true else CheckFileType=false
next
case "bmp"
stamp=fstream.read(2)
for i=0 to 1
if ascB(MidB(stamp,i+1,1))=bmp(i) then CheckFileType=true else CheckFileType=false
next
end select
fstream.Close
set fseteam=nothing
if err.number<>0 then CheckFileType=false
end function
%>
那么在应用的时候
CheckFileType(server.mappath("cnbruce.jpg"))
或者
CheckFileType("F:/web/164/images/cnbruce.jpg"))
反正即是检测验证本地物理地址的图像文件类型，返回 true 或 false值
所以这个情况应用在图像上传中，目前的办法是先允许该“伪图像”文件的上传，接着使用以上的自定义函数判断该文件是否符合图像的规范，若是木马伪装的图像文件则FSO删除之，比如：
file.SaveAs Server.mappath(filename) '保存文件
If not CheckFileType(Server.mappath(filename)) then
response.write "错误的图像格式"
Set fso = CreateObject("Scripting.FileSystemObject")
Set ficn = fso.GetFile(Server.mappath(filename))
ficn.delete
set ficn=nothing
set fso=nothing
response.end
end if
则是先将文件上传，接着立马使用自定义函数判断文件图像类型的吻合性，FSO做出删除该文件的操作。
ASP上传漏洞还利用"\0"对filepath进行手脚操作
http://www.21kn.com/htmldata/2006-05-14/1147569636.html
针对这样的情况可使用如下函数
function TrueStr(fileTrue)
str_len=len(fileTrue)
pos=Instr(fileTrue,chr(0))
if pos=0 or pos=str_len then
TrueStr=true
else
TrueStr=false
end if
end function
接着就可判断后再做文件的上传
if TrueStr(filename)=false then
response.write "非法文件"
response.end
end if
file.SaveAs Server.mappath(filename)
关于upfile.asp的全新内容如下：
<%@LANGUAGE="VBSCRIPT" CODEPAGE="936"%>
<!--#include file="upload.inc"-->
<html>
<head>
<title>文件上传</title>
<meta http-equiv="content-type" content="text/html;charset=gb2312">
</head>
<body>
<%
on error resume next
dim upload,f_folder,file,formPath,iCount,filename,fileExt,filesizemin,filesizemax
'***************************************
'CheckFileType 函数用来检查文件是否为图片文件
'参数filename是本地文件的路径
'如果是文件jpeg,gif,bmp,png图片中的一种，函数返回true，否则返回false
'**************************************
const adTypeBinary=1
dim jpg(1):jpg(0)=CByte(&HFF):jpg(1)=CByte(&HD8)
dim bmp(1):bmp(0)=CByte(&H42):bmp(1)=CByte(&H4D)
dim png(3):png(0)=CByte(&H89):png(1)=CByte(&H50):png(2)=CByte(&H4E):png(3)=CByte(&H47)
dim gif(5):gif(0)=CByte(&H47):gif(1)=CByte(&H49):gif(2)=CByte(&H46):gif(3)=CByte(&H39):gif(4)=CByte(&H38):gif(5)=CByte(&H61)
function CheckFileType(filename)
CheckFileType=false
dim fstream,fileExt,stamp,i
fileExt=mid(filename,InStrRev(filename,".")+1)
set fstream=Server.createobject("ADODB.Stream")
fstream.Open
fstream.Type=adTypeBinary
fstream.LoadFromFile filename
fstream.position=0
select case fileExt
case "jpg","jpeg"
stamp=fstream.read(2)
for i=0 to 1
if ascB(MidB(stamp,i+1,1))=jpg(i) then CheckFileType=true else CheckFileType=false
next
case "gif"
stamp=fstream.read(6)
for i=0 to 5
if ascB(MidB(stamp,i+1,1))=gif(i) then CheckFileType=true else CheckFileType=false
next
case "png"
stamp=fstream.read(4)
for i=0 to 3
if ascB(MidB(stamp,i+1,1))=png(i) then CheckFileType=true else CheckFileType=false
next
case "bmp"
stamp=fstream.read(2)
for i=0 to 1
if ascB(MidB(stamp,i+1,1))=bmp(i) then CheckFileType=true else CheckFileType=false
next
end select
fstream.Close
set fseteam=nothing
if err.number<>0 then CheckFileType=false
end function
function TrueStr(fileTrue)
str_len=len(fileTrue)
pos=Instr(fileTrue,chr(0))
if pos=0 or pos=str_len then
TrueStr=true
else
TrueStr=false
end if
end function
filesizemin=100
filesizemax=200*1024
set upload=new upload_5xSoft '建立上传对象
f_folder=upload.form("upfilefolder")
'*******列出所有上传文件***********
For each formName in upload.objFile
set file=upload.file(formName)
If file.filesize>0 then
'********检测文件大小***********
If file.filesize<filesizemin Then
response.write "你上传的文件太小了 [ <a href=# onclick=history.go(-1)>重新上传</a> ]"
ElseIf file.filesize>filesizemax then
response.write "文件大小超过了 "&filesizemax&"字节 限制 [ <a href=# onclick=history.go(-1)>重新上传</a> ]"
End If
'*******检测文件类型*******
fileExt=ucase(right(file.filename,4))
uploadsuc=false Forum_upload="RAR|ZIP|SWF|JPG|PNG|GIF|DOC|TXT|CHM|PDF|ACE|MP3|WMA|WMV|MIDI|AVI|RM|RA|RMVB|MOV|XLS"
Forumupload=split(Forum_upload,"|")
for i=0 to ubound(Forumupload)
if fileEXT="."&trim(Forumupload(i)) then
uploadsuc=true
exit for
else
uploadsuc=false
end if
next
if uploadsuc=false then
response.write "文件格式不正确 [ <a href=# onclick=history.go(-1)>重新上传</a> ]"
response.end
end if
'********建立文件上传的目录文件夹*********
Set upf=Server.CreateObject("Scripting.FileSystemObject")
If Err<>0 Then
Err.Clear
response.write("您的服务器不支持FSO")
response.end
End If
f_type= replace(fileExt,".","")
f_name= year(now)&"-"&month(now)
If upf.FolderExists(Server.MapPath(f_folder&"/"&f_type&"/"&f_name))=False Then
If upf.FolderExists(Server.MapPath(f_folder&"/"&f_type))=False Then
If upf.FolderExists(Server.MapPath(f_folder))=False Then
upf.CreateFolder Server.MapPath(f_folder)
upf.CreateFolder Server.MapPath(f_folder&"/"&f_type)
upf.CreateFolder Server.MapPath(f_folder&"/"&f_type&"/"&f_name)
Else
upf.CreateFolder Server.MapPath(f_folder&"/"&f_type)
upf.CreateFolder Server.MapPath(f_folder&"/"&f_type&"/"&f_name)
End If
Else
upf.CreateFolder Server.MapPath(f_folder&"/"&f_type&"/"&f_name)
End If
End If
f_ftn=f_folder&"/"&f_type&"/"&f_name
Set upf=Nothing
'********保存上传文件至文件夹********
randomize
ranNum=int(90000*rnd)+10000
filename=f_ftn&"/"&day(now)&"-"&ranNum&"-"&file.filename
if TrueStr(filename)=false then
response.write "非法文件"
response.end
end if
if file.filesize>filesizemin and file.filesize<filesizemax then
file.SaveAs Server.mappath(filename) '保存文件
If not CheckFileType(Server.mappath(filename)) then
response.write "错误的图像格式"
Set fso = CreateObject("Scripting.FileSystemObject")
Set ficn = fso.GetFile(Server.mappath(filename))
ficn.delete
set ficn=nothing
set fso=nothing
response.end
end if
if f_type="JPG" or f_type="GIF" or f_type="PNG" then
response.write "<script>parent.cn_bruce.cn_content.value+='[img]"&filename&"[/img]'</script>"
ElseIf f_type="ZIP" or f_type="RAR" or f_type="DOC" or f_type="TXT" then
response.write "<script>parent.cn_bruce.cn_content.value+='[url]"&filename&"[/url]'</script>"
'ElseIf
else
response.write "<script>parent.cn_bruce.cn_content.value+=' "&filename&" '</script>"
end if
iCount=iCount+1
end if
set file=nothing
end if
next
set upload=nothing '删除此对象
response.write (iCount&" 个文件上传成功! <a href=# onclick=history.go(-1)>继续上传</a>")
%>
</body>
</html>
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