OSEC

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From: Auriemma Luigi (aluigi_at_pivx.com)
Date: Thu Aug 22 2002 - 16:18:08 CDT

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    Auriemma Luigi, PivX security advisory

    Application: Abyss webserver (http://www.aprelium.com)
    Version: 1.0.3 (patch 2) and previous, both Windows and Linux,
                 (patch 2) fix the administration bug
    Bug: Directory traversal and administration bugs
    Risk (high): An attacker can view every file in the remote system and
                 he can administrate the Abyss server without any login.
                 Read Bug section for have more details
    Author: Auriemma Luigi, Security Researcher, PivX Solutions, LLC
                 e-mail: aluigipivx.com

    ######################################################################

    1) Introduction
    2) Bug
    3) The Code
    4) Fix
    5) Philosophy

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    ----------------------------------------------------------------------

    1) Introduction

    Abyss is a free webserver that runs on Win32 and Linux x86 systems.
    It is tiny and it has some interesting features like for example the
    use of a "console" for administrate the server remotely.
    Unfortunately the usage of this console is the most dangerous thing in
    this webserver because an attacker can do what he want without any
    password.
    This bug was found by Aprelium in June and has been fixed in the
    patch 2 release. However a misunderstanding with CNET have limited the
    diffusion of this version.

    The other bug is another dangerous problem: directory traversal bug.
    The last problem is a minor vulnerability in the management of files
    with some characters added at the end.

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    2) Bug

    A] Directory traversal bug
    ==========================

    The first problem I want to show, is about viewing all the files in
    the systems where Abyss 1.0.3 (patch 2) and previous run.

    This problem is caused by the character '\' (%5c) that is not checked
    as bad character, so the server follow the path in the URI that the
    attacker give until it reach the file requested.

    The following are two simple examples for see the winnt\win.ini file:

    http://host/%5c%2e%2e%5c%2e%2e%5c%2e%2e%5c%2e%2e%5cwinnt%5cwin.ini
    "GET /\..\..\..\..\..\winnt\win.ini HTTP/1.0"

    This last is an HTTP request that can be sent with telnet because
    some browsers can modify the "\.." chars.

    It is also possible to view the index of the directories (but not the
    root) ONLY if the AutoIndex option is not disabled (default is
    enable).
    This is for view winnt:
    http://host/%5c%2e%2e%5c%2e%2e%5c%2e%2e%5c%2e%2e%5cwinnt/

    In Linux fortunally the attacker cannot go down to the path, but he
    can go only in the Abyss folder and see SOME files like, for example,
    the files in cgi-bin and chl directory but NOT the abyss.conf or the
    logs (this is the same also on Windows).
    Two simple example are:

    http://host/%2f%2e%2e%2f
    http://host/%2f%2e%2e%2fcgi-bin/

    and we will see the index of the Abyss and cgi-bin folder.

    B] Administration bug (fixed in patch 2 release)
    ================================================

    The console used in Abyss is the same web server that is binded to
    port 9999 (another default port can be the 81) and look to the files
    in the CHL directory of the server.
    In this directory there are all the files to manage the server
    remotely so the administrator can change the parameters without
    modifing the abyss.conf file manually.

    This bug is really incredible... an attacker without login can
    reconfigure every parameter of the server.
    Some examples of what the attacker can do are:
    - Stop, Run and Halt the server
    - change username and password of the administrator
    - change all the advanced parameters of the server (log files, number
      of requests, etc...)
    - all the thing that the real administrator can do

    The only limit for the attacker is that he cannot know the current
    settings of the server, but I think that it is not so important
    because he can redefine all!
    Remember that the attacker can redifine the administrator login and
    he will be the real administrator.

    The proof-of-concept can be downloaded from my userpage:
    http://www.pivx.com/luigi/poc/abyss-adm.zip

    C] Characters adding
    ====================

    This is a problem that is diffused on almost all the Windows
    applications and not only.

    The problem is that adding some characters (in this case the '+') the
    attacker can read "for example" the .chl files bypassing the login.
    Not a bad bug, but is better to fix bugs like this before they can be
    used for more dangerous exploitations.

    Simple examples are:

    http://host:9999/srvstatus.chl+
    http://host:9999/consport.chl+
    http://host:9999/conspass.chl+
    http://host:9999/general.chl+

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    ----------------------------------------------------------------------

    3) The Code

    A] Example of the directory traversal bug on Win:

    http://host/%5c%2e%2e%5c%2e%2e%5c%2e%2e%5c%2e%2e%5cwinnt%5cwin.ini
    "GET /\..\..\..\..\..\winnt\win.ini HTTP/1.0"

    Abyss index on Linux:

    http://host/%2f%2e%2e%2f

    B] For the administration bug watch the html file in my userpage
    http://www.pivx.com/luigi/poc/abyss-adm.zip

    It can be used to test the server that run on the same machine, at
    the address 127.0.0.1.
    If you want to test other machines simply replace the string
    "http://127.0.0.1:9999" at line 4 of the html with the host and the
    port you want.

    C] Add the '+' char at the end of the file requested.

    ______________________________________________________________________
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    4) Fix

    Abyss 1.0.3 (patch 3) from the Aprelium web-site:
    http://www.aprelium.com

    or directly the updated executable:
    http://www.aprelium.com/news/patch1033.html

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    5) Philosophy

    I'm really hopeful about the FULL-DISCLOSURE policy, because with it
    "everyone" can know the real effects of an attack, the real danger of
    a bug, someone can learn a bit of creative programming (I have learned
    a bit of interesting C from the source code of some published
    exploits) and it's useful for all the people that are hopeful in this
    type of disclosure.
    No secrets!

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    About PivX Solutions
    PivX Solutions, is a premier network security consultancy offering a
    myriad of network security services to our clients, the most notable
    being our proprietary Risk and Vulnerability Assessment (RAVA).
    Dedicated PivX founders have also developed the patented Invisiwall
    network security device which offers the most comprehensive and secure
    intrusion detection system available.

    For more information go to http://www.PivX.com

     

    Any type of feedback is really welcome!

    Byez

    -- 
    PivX Security Researcher