ASP Submission

Posted on 2014-09-22
Medium Priority
Last Modified: 2014-10-05
Hi Experts,

 Is it possible when a form is submitted to a ASP page, that ASP page to check the absolute path of the form page?

 In other words, I have just noticed some invalid data I have been validating with JavaScript, and found out that someone has view source, saved it on the local machine, tampered with the JavaScript and adjusted the form action to the ASP's absolute URL.

 So, if I can verify the absolute URL of the page being submitted (without using hidden fields, of course), then I can avoid this.

Question by:APD_Toronto
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LVL 33

Accepted Solution

Big Monty earned 668 total points
ID: 40336919
you'll probably want to look into using Request.ServerVariables


Specifically, you could use the SCRIPT_NAME or even REMOTE_ADDR variables to do your check. I would probably use REMOTE_ADDR as that should return the actual IP address of the page making the request
LVL 58

Assisted Solution

Gary earned 668 total points
ID: 40336999

Author Comment

ID: 40337036
So, REMOTE_ADDR will, return the IP of the form page, NOT the visitor?
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LVL 58

Expert Comment

ID: 40337042
REMOTE_ADDR is pointless as is SCRIPT_NAME
LVL 33

Expert Comment

by:Big Monty
ID: 40337366
So, REMOTE_ADDR will, return the IP of the form page, NOT the visitor?
that is correct. Although you could run into issues if the user is behind a proxy server. You could also try using HTTP_X_FORWARDED_FOR, but again, it's not 100%, but it can help out some.

you may also want to look into using Captcha - http://www.captcha.net/

REMOTE_ADDR is pointless as is SCRIPT_NAME

why is that? because you said so? as someone with an elevated status here at EE, I wouldn't expect you to post such a blanket statement like that without providing some kind of data to back up your claims. If the visiting user isn't behind I proxy, it'll return the proper IP address. Using SCRIPT_NAME isn't "useless" as you suggest either. If someone is just copying and pasting the downloaded source, and they don't figure to save it to the same filename, it's a decent enough check. I wouldn't use it by itself, but it's still a viable option to use in conjunction with other techniques
LVL 33

Expert Comment

by:Big Monty
ID: 40337367
So, REMOTE_ADDR will, return the IP of the form page, NOT the visitor?

forgot to ask, but how are users logging in? if your're using windows authentication then you can grab the user name of the person logged in
LVL 58

Expert Comment

ID: 40337369
REMOTE_ADDR returns the remote IP of the pc/proxy accessing the site - what good is that to verify the form was filled in online and not posted remotely?

SCRIPT_NAME returns the name of the page being currently accessed - what good is that to verify the form was filled in online and not posted remotely?
LVL 53

Assisted Solution

by:Scott Fell, EE MVE
Scott Fell,  EE MVE earned 664 total points
ID: 40337479
On form page
<!-- #include virtual ="sha.asp" --> 

if request.form = "" then  ' no form submit
   tstamp = now()
   passcode = Session.SessionID & tstamp & "some_secret_word"
end if
<input type="hidden" name="stamp" value="<%=tstamp%>">
<input type="hidden" name="passcode" value="<%=sha(passcode)%>">


Open in new window

on submit page
<!-- #include virtual ="sha.asp" --> 
if request.form<>"" then
     if request.form("passcode")=  sha(Session.SessionID&request.form("stamp")&"some_secret_word") then ' ok to process form

end if

Open in new window

Since you now know the time stamp, you can also make sure the form is submitted within a few seconds
LVL 53

Expert Comment

by:Scott Fell, EE MVE
ID: 40337485
Here is a sha256 function.

On this one, you call by using sha256("foobar")

Save it in a file called sha256.asp and put it at the top or bottom of your page via an include file.  

' See the VB6 project that accompanies this sample for full code comments on how
' it works.
' ASP VBScript code for generating a SHA256 'digest' or 'signature' of a string. The
' MD5 algorithm is one of the industry standard methods for generating digital
' signatures. It is generically known as a digest, digital signature, one-way
' encryption, hash or checksum algorithm. A common use for SHA256 is for password
' encryption as it is one-way in nature, that does not mean that your passwords
' are not free from a dictionary attack. 
' If you are using the routine for passwords, you can make it a little more secure
' by concatenating some known random characters to the password before you generate
' the signature and on subsequent tests, so even if a hacker knows you are using
' SHA-256 for your passwords, the random characters will make it harder to dictionary
' attack.
' NOTE: Due to the way in which the string is processed the routine assumes a
' single byte character set. VB passes unicode (2-byte) character strings, the
' ConvertToWordArray function uses on the first byte for each character. This
' has been done this way for ease of use, to make the routine truely portable
' you could accept a byte array instead, it would then be up to the calling
' routine to make sure that the byte array is generated from their string in
' a manner consistent with the string type.
' This is 'free' software with the following restrictions:
' You may not redistribute this code as a 'sample' or 'demo'. However, you are free
' to use the source code in your own code, but you may not claim that you created
' the sample code. It is expressly forbidden to sell or profit from this source code
' other than by the knowledge gained or the enhanced value added by your own code.
' Use of this software is also done so at your own risk. The code is supplied as
' is without warranty or guarantee of any kind.
' Should you wish to commission some derivative work based on this code provided
' here, or any consultancy work, please do not hesitate to contact us.
' Web Site:  http://www.frez.co.uk
' E-mail:    sales@frez.co.uk

Private m_lOnBits(30)
Private m_l2Power(30)
Private K(63)

Private Const BITS_TO_A_BYTE = 8
Private Const BYTES_TO_A_WORD = 4
Private Const BITS_TO_A_WORD = 32

m_lOnBits(0) = CLng(1)
m_lOnBits(1) = CLng(3)
m_lOnBits(2) = CLng(7)
m_lOnBits(3) = CLng(15)
m_lOnBits(4) = CLng(31)
m_lOnBits(5) = CLng(63)
m_lOnBits(6) = CLng(127)
m_lOnBits(7) = CLng(255)
m_lOnBits(8) = CLng(511)
m_lOnBits(9) = CLng(1023)
m_lOnBits(10) = CLng(2047)
m_lOnBits(11) = CLng(4095)
m_lOnBits(12) = CLng(8191)
m_lOnBits(13) = CLng(16383)
m_lOnBits(14) = CLng(32767)
m_lOnBits(15) = CLng(65535)
m_lOnBits(16) = CLng(131071)
m_lOnBits(17) = CLng(262143)
m_lOnBits(18) = CLng(524287)
m_lOnBits(19) = CLng(1048575)
m_lOnBits(20) = CLng(2097151)
m_lOnBits(21) = CLng(4194303)
m_lOnBits(22) = CLng(8388607)
m_lOnBits(23) = CLng(16777215)
m_lOnBits(24) = CLng(33554431)
m_lOnBits(25) = CLng(67108863)
m_lOnBits(26) = CLng(134217727)
m_lOnBits(27) = CLng(268435455)
m_lOnBits(28) = CLng(536870911)
m_lOnBits(29) = CLng(1073741823)
m_lOnBits(30) = CLng(2147483647)

m_l2Power(0) = CLng(1)
m_l2Power(1) = CLng(2)
m_l2Power(2) = CLng(4)
m_l2Power(3) = CLng(8)
m_l2Power(4) = CLng(16)
m_l2Power(5) = CLng(32)
m_l2Power(6) = CLng(64)
m_l2Power(7) = CLng(128)
m_l2Power(8) = CLng(256)
m_l2Power(9) = CLng(512)
m_l2Power(10) = CLng(1024)
m_l2Power(11) = CLng(2048)
m_l2Power(12) = CLng(4096)
m_l2Power(13) = CLng(8192)
m_l2Power(14) = CLng(16384)
m_l2Power(15) = CLng(32768)
m_l2Power(16) = CLng(65536)
m_l2Power(17) = CLng(131072)
m_l2Power(18) = CLng(262144)
m_l2Power(19) = CLng(524288)
m_l2Power(20) = CLng(1048576)
m_l2Power(21) = CLng(2097152)
m_l2Power(22) = CLng(4194304)
m_l2Power(23) = CLng(8388608)
m_l2Power(24) = CLng(16777216)
m_l2Power(25) = CLng(33554432)
m_l2Power(26) = CLng(67108864)
m_l2Power(27) = CLng(134217728)
m_l2Power(28) = CLng(268435456)
m_l2Power(29) = CLng(536870912)
m_l2Power(30) = CLng(1073741824)
K(0) = &H428A2F98
K(1) = &H71374491
K(2) = &HB5C0FBCF
K(3) = &HE9B5DBA5
K(4) = &H3956C25B
K(5) = &H59F111F1
K(6) = &H923F82A4
K(7) = &HAB1C5ED5
K(8) = &HD807AA98
K(9) = &H12835B01
K(10) = &H243185BE
K(11) = &H550C7DC3
K(12) = &H72BE5D74
K(13) = &H80DEB1FE
K(14) = &H9BDC06A7
K(15) = &HC19BF174
K(16) = &HE49B69C1
K(17) = &HEFBE4786
K(18) = &HFC19DC6
K(19) = &H240CA1CC
K(20) = &H2DE92C6F
K(21) = &H4A7484AA
K(22) = &H5CB0A9DC
K(23) = &H76F988DA
K(24) = &H983E5152
K(25) = &HA831C66D
K(26) = &HB00327C8
K(27) = &HBF597FC7
K(28) = &HC6E00BF3
K(29) = &HD5A79147
K(30) = &H6CA6351
K(31) = &H14292967
K(32) = &H27B70A85
K(33) = &H2E1B2138
K(34) = &H4D2C6DFC
K(35) = &H53380D13
K(36) = &H650A7354
K(37) = &H766A0ABB
K(38) = &H81C2C92E
K(39) = &H92722C85
K(40) = &HA2BFE8A1
K(41) = &HA81A664B
K(42) = &HC24B8B70
K(43) = &HC76C51A3
K(44) = &HD192E819
K(45) = &HD6990624
K(46) = &HF40E3585
K(47) = &H106AA070
K(48) = &H19A4C116
K(49) = &H1E376C08
K(50) = &H2748774C
K(51) = &H34B0BCB5
K(52) = &H391C0CB3
K(53) = &H4ED8AA4A
K(54) = &H5B9CCA4F
K(55) = &H682E6FF3
K(56) = &H748F82EE
K(57) = &H78A5636F
K(58) = &H84C87814
K(59) = &H8CC70208
K(60) = &H90BEFFFA
K(61) = &HA4506CEB
K(62) = &HBEF9A3F7
K(63) = &HC67178F2

Private Function LShift(lValue, iShiftBits)
    If iShiftBits = 0 Then
        LShift = lValue
        Exit Function
    ElseIf iShiftBits = 31 Then
        If lValue And 1 Then
            LShift = &H80000000
            LShift = 0
        End If
        Exit Function
    ElseIf iShiftBits < 0 Or iShiftBits > 31 Then
        Err.Raise 6
    End If
    If (lValue And m_l2Power(31 - iShiftBits)) Then
        LShift = ((lValue And m_lOnBits(31 - (iShiftBits + 1))) * m_l2Power(iShiftBits)) Or &H80000000
        LShift = ((lValue And m_lOnBits(31 - iShiftBits)) * m_l2Power(iShiftBits))
    End If
End Function

Private Function RShift(lValue, iShiftBits)
    If iShiftBits = 0 Then
        RShift = lValue
        Exit Function
    ElseIf iShiftBits = 31 Then
        If lValue And &H80000000 Then
            RShift = 1
            RShift = 0
        End If
        Exit Function
    ElseIf iShiftBits < 0 Or iShiftBits > 31 Then
        Err.Raise 6
    End If
    RShift = (lValue And &H7FFFFFFE) \ m_l2Power(iShiftBits)
    If (lValue And &H80000000) Then
        RShift = (RShift Or (&H40000000 \ m_l2Power(iShiftBits - 1)))
    End If
End Function

Private Function AddUnsigned(lX, lY)
    Dim lX4
    Dim lY4
    Dim lX8
    Dim lY8
    Dim lResult
    lX8 = lX And &H80000000
    lY8 = lY And &H80000000
    lX4 = lX And &H40000000
    lY4 = lY And &H40000000
    lResult = (lX And &H3FFFFFFF) + (lY And &H3FFFFFFF)
    If lX4 And lY4 Then
        lResult = lResult Xor &H80000000 Xor lX8 Xor lY8
    ElseIf lX4 Or lY4 Then
        If lResult And &H40000000 Then
            lResult = lResult Xor &HC0000000 Xor lX8 Xor lY8
            lResult = lResult Xor &H40000000 Xor lX8 Xor lY8
        End If
        lResult = lResult Xor lX8 Xor lY8
    End If
    AddUnsigned = lResult
End Function

Private Function Ch(x, y, z)
    Ch = ((x And y) Xor ((Not x) And z))
End Function

Private Function Maj(x, y, z)
    Maj = ((x And y) Xor (x And z) Xor (y And z))
End Function

Private Function S(x, n)
    S = (RShift(x, (n And m_lOnBits(4))) Or LShift(x, (32 - (n And m_lOnBits(4)))))
End Function

Private Function R(x, n)
    R = RShift(x, CInt(n And m_lOnBits(4)))
End Function

Private Function Sigma0(x)
    Sigma0 = (S(x, 2) Xor S(x, 13) Xor S(x, 22))
End Function

Private Function Sigma1(x)
    Sigma1 = (S(x, 6) Xor S(x, 11) Xor S(x, 25))
End Function

Private Function Gamma0(x)
    Gamma0 = (S(x, 7) Xor S(x, 18) Xor R(x, 3))
End Function

Private Function Gamma1(x)
    Gamma1 = (S(x, 17) Xor S(x, 19) Xor R(x, 10))
End Function

Private Function ConvertToWordArray(sMessage)
    Dim lMessageLength
    Dim lNumberOfWords
    Dim lWordArray()
    Dim lBytePosition
    Dim lByteCount
    Dim lWordCount
    Dim lByte
    Const MODULUS_BITS = 512
    Const CONGRUENT_BITS = 448
    lMessageLength = Len(sMessage)
    ReDim lWordArray(lNumberOfWords - 1)
    lBytePosition = 0
    lByteCount = 0
    Do Until lByteCount >= lMessageLength
        lWordCount = lByteCount \ BYTES_TO_A_WORD
        lBytePosition = (3 - (lByteCount Mod BYTES_TO_A_WORD)) * BITS_TO_A_BYTE
        lByte = AscB(Mid(sMessage, lByteCount + 1, 1))
        lWordArray(lWordCount) = lWordArray(lWordCount) Or LShift(lByte, lBytePosition)
        lByteCount = lByteCount + 1

    lWordCount = lByteCount \ BYTES_TO_A_WORD
    lBytePosition = (3 - (lByteCount Mod BYTES_TO_A_WORD)) * BITS_TO_A_BYTE

    lWordArray(lWordCount) = lWordArray(lWordCount) Or LShift(&H80, lBytePosition)

    lWordArray(lNumberOfWords - 1) = LShift(lMessageLength, 3)
    lWordArray(lNumberOfWords - 2) = RShift(lMessageLength, 29)
    ConvertToWordArray = lWordArray
End Function

Public Function SHA256(sMessage)
    Dim HASH(7)
    Dim M
    Dim W(63)
    Dim a
    Dim b
    Dim c
    Dim d
    Dim e
    Dim f
    Dim g
    Dim h
    Dim i
    Dim j
    Dim T1
    Dim T2
    HASH(0) = &H6A09E667
    HASH(1) = &HBB67AE85
    HASH(2) = &H3C6EF372
    HASH(3) = &HA54FF53A
    HASH(4) = &H510E527F
    HASH(5) = &H9B05688C
    HASH(6) = &H1F83D9AB
    HASH(7) = &H5BE0CD19
    M = ConvertToWordArray(sMessage)
    For i = 0 To UBound(M) Step 16
        a = HASH(0)
        b = HASH(1)
        c = HASH(2)
        d = HASH(3)
        e = HASH(4)
        f = HASH(5)
        g = HASH(6)
        h = HASH(7)
        For j = 0 To 63
            If j < 16 Then
                W(j) = M(j + i)
                W(j) = AddUnsigned(AddUnsigned(AddUnsigned(Gamma1(W(j - 2)), W(j - 7)), Gamma0(W(j - 15))), W(j - 16))
            End If
            T1 = AddUnsigned(AddUnsigned(AddUnsigned(AddUnsigned(h, Sigma1(e)), Ch(e, f, g)), K(j)), W(j))
            T2 = AddUnsigned(Sigma0(a), Maj(a, b, c))
            h = g
            g = f
            f = e
            e = AddUnsigned(d, T1)
            d = c
            c = b
            b = a
            a = AddUnsigned(T1, T2)
        HASH(0) = AddUnsigned(a, HASH(0))
        HASH(1) = AddUnsigned(b, HASH(1))
        HASH(2) = AddUnsigned(c, HASH(2))
        HASH(3) = AddUnsigned(d, HASH(3))
        HASH(4) = AddUnsigned(e, HASH(4))
        HASH(5) = AddUnsigned(f, HASH(5))
        HASH(6) = AddUnsigned(g, HASH(6))
        HASH(7) = AddUnsigned(h, HASH(7))
    SHA256 = LCase(Right("00000000" & Hex(HASH(0)), 8) & Right("00000000" & Hex(HASH(1)), 8) & Right("00000000" & Hex(HASH(2)), 8) & Right("00000000" & Hex(HASH(3)), 8) & Right("00000000" & Hex(HASH(4)), 8) & Right("00000000" & Hex(HASH(5)), 8) & Right("00000000" & Hex(HASH(6)), 8) & Right("00000000" & Hex(HASH(7)), 8))
End Function

Open in new window


Author Comment

ID: 40339878
Any objections re HTTP_REFERER?

I noticed that when I submit from my server the full URL is returned; when I submit from a local file, I get an empty string.  So I can just test for that.

Any drawbacks here?
LVL 58

Expert Comment

ID: 40339886
Referer can be spoofed.

Author Comment

ID: 40339904
@Gary, what do you mean?

Author Comment

ID: 40339952
...how can it be spoofed?
LVL 58

Expert Comment

ID: 40339964

Author Comment

ID: 40339982
Any alternates?

Author Comment

ID: 40339990
What about restricting users by Remote IP
LVL 58

Expert Comment

ID: 40339998
Knowing their IP isn't going to help

Author Comment

ID: 40340006
With the remote ip, I'll just restrict inner-office, would that work

Also, I do have full access to the server, can I use that to my advantage? Like saving a file from the form pg, then accessing it from the process pg?
LVL 58

Expert Comment

ID: 40340015
If you know the IP then that is the easiest method, first time you said this was intra office.
LVL 53

Expert Comment

by:Scott Fell, EE MVE
ID: 40340032
Read up on Cross-Site Request Forgery


There is nothing built in for this with classic asp and you have to do it manually.  

A captcha as BM mentioned could help as would generating a key as I outlined.
LVL 53

Expert Comment

by:Scott Fell, EE MVE
ID: 40340095
If this is for inside your office, why not just create password or use the active directory to auto log on?

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