asp.netsecuritysubstringindexoutofboundsexceptionrequest.servervariables

ASP.Net System.ArgumentOutOfRangeException

So I have some code running an IP check to ensure an ADMIN account cannot have access from outside my network.

string strIP = Request.ServerVariables["REMOTE_ADDR"];
if (
    (strIP.Substring(0, 9) != "XXX.XX.X.")
&&  (strIP.Substring(0, 10) != "XXX.XX.XX.")
&&  (strIP.Substring(0, 6) != "XX.XX.")
&&  (strIP.Substring(0, 6) != "XX.XX.")
)
{
..// Check user for being an ADMIN // ....
}

This code was working fine for several weeks, but suddenly has started consistently to err out. The error message is:

Exception

Exception Type: System. ArgumentOUtOfRangeException

Exception Message: Index and length must refer to a location within the string. Parameter name: length.

When I remove the line with "Substring(0,10)", everything works. Also, when I change the line "Substring(0,10)" to "Substring(0,9)" and remove the last ".", everything works.

Can anyone tell me why or perhaps instruct on what is being done incorrectly? For the life of me I can't figure out what is going on.

Solution

  • The problem is that strIP doesn't have 10 characters because your configuration changed for some reason. You could do something like:

    (strIP.Length >= 9 && strIP.Substring(0, 9) != "XXX.XX.X.")
||  (strIP.Length >= 10 && strIP.Substring(0, 10) != "XXX.XX.XX.")
||  (strIP.Length >= 6 && strIP.Substring(0, 6) != "XX.XX.")

    Notice that the fourth line was a duplicate of the third.