[ISN] Yet another IIS exploit reported

From: InfoSec News (isnat_private)
Date: Wed May 16 2001 - 00:30:01 PDT

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    By: Thomas C Greene in Washington
    Posted: 16/05/2001 at 06:32 GMT
    It's been a rough two weeks for IIS security. On 1 May it was our
    solemn duty to report the IIS .printer ISAPI vulnerability; on 8 May
    we reported the sadmind/IIS worm; and today we have to inform you of a
    brand new stuff-up affecting IIS 4.0 and 5.0, handily exploited with a
    simple Unicode trick.
    An easily malformed file name can be used to load an executable CGI
    program through a double-decoding glitch in IIS.
    When an obfuscated file name passes the first decoding -- which, among
    other things, searches for .com and .exe extensions -- a second,
    superfluous decoding restores the name and grants access to the
    executable file, handily enabling an attacker to carry out a directory
    traversal and run arbitrary code outside the Web directory.
    The vulnerability enables the execution of arbitrary code, denial of
    service attacks, and data disclosure -- which is a total drag if you
    have a file full of credit card details somewhere on your server.
    The hole was originally discovered by nsfocus on 27 March. After
    several delays requested by Microsoft, the announcement was finally
    made on 15 May.
    It's similar to the hole exploited by the sadmind/IIS worm, but
    potentially more malicious. Lord knows it won't be long before we see
    this one similarly automated.
    Best get those patches in place straight away.
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