Monthly Archives: July 2010

IIS5.1 Directory Authentication Bypass by using “:$I30:$Index_Allocation”

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Although IIS5 is very old, finding one is not impossible! Therefore, I want to introduce a technique to bypass the IIS authentication methods on a directory.
This vulnerability is because of using Alternate Data Stream to open a protected folder.
All of IIS authentication methods can be circumvented. In this technique, we can add a “:$i30:$INDEX_ALLOCATION” to a directory name to bypass the authentication.
In a protected folder such as “AuthNeeded” which includes “secretfile.asp”:
It is possible to run “secretfile.asp” by using:
Instead of:

More description:
Why IIS6 and 7 are not vulnerable:
– In these versions, IIS does not accept colon (“:”) character from the URL before the querystring.

Why we cannot use “::$Data” in IIS 5.1 anymore:
– IIS rejects the request if its URL contains “::$” (before querystring).

Why IIS5 is vulnerable to “Directory Authentication Bypass” by using “:$I30:$Index_Allocation”:
– IIS only verifies the directory name to check for authentication. Therefore, we can use “$I30:$Index_Allocation/” instead of “” to bypass the authentication.

Is it possible to bypass something else by using “:$I30:$Index_Allocation” on a NTFS partition:
– If a checking is only based on the directory name, it can be bypassed by using this method.

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