How to Pass Unsafe Characters in a URL (153545)


The information in this article applies to:

  • Microsoft Internet Information Server 1.0
  • Microsoft Internet Information Server 2.0
  • Microsoft Internet Information Server 3.0
  • Microsoft Internet Information Server 4.0
This article was previously published under Q153545
We strongly recommend that all users upgrade to Microsoft Internet Information Services (IIS) version 6.0 running on Microsoft Windows Server 2003. IIS 6.0 significantly increases Web infrastructure security. For more information about IIS security-related topics, visit the following Microsoft Web site:

http://www.microsoft.com/technet/security/prodtech/IIS.mspx

SUMMARY

It is possible to pass unsafe characters in a URL by encoding the characters using the following syntax:

% HEX

where HEX is the hexadecimal value of the unsafe character, for example, %2B.

MORE INFORMATION

For example: ASCII TABLE

ASCIIHEXENCODED
+2B%2B
?3F%3F

+ URL: http://server/scripts/script.idc?Param=2+2
ENCODED URL: http://server/scripts/script.idc?Param=2%3F2

? URL: http://server/scripts/script.idc?Param=Who?
ENCODED URL: http://server/scripts/script.idc?Param=Who%2B

RFC 1738 discusses "unsafe characters" in more detail below.

Unsafe:

Characters can be unsafe for a number of reasons. The space character is unsafe because significant spaces may disappear and insignificant spaces may be introduced when URLs are transcribed or typeset or subjected to the treatment of word-processing programs. The chevron characters, < and >, are unsafe because they are used as the delimiters around URLs in free text; the quotation mark (""") is used to delimit URLs in some systems. The character # is unsafe and should always be encoded because it is used in World Wide Web and in other systems to delimit a URL from a fragment/anchor identifier that might follow it. The character % is unsafe because it is used for encodings of other characters. Other characters are unsafe because gateways and other transport agents are known to sometimes modify such characters. These characters are {, }, |, \, ^, ~, [, ], and `.

All unsafe characters must always be encoded within a URL. For example, the character # must be encoded within URLs even in systems that do not normally deal with fragment or anchor identifiers, so that if the URL is copied into another system that does use them, it will not be necessary to change the URL encoding.

Modification Type:MinorLast Reviewed:6/22/2005
Keywords:kbhowto KB153545
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