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                             Luigi Auriemma

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
             he can administrate the Abyss server without any login.
             Read the "Bug" section for have more details
Date:        22 Aug 2002
Author:      Luigi Auriemma
             e-mail: aluigi@autistici.org
             web:    aluigi.org

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


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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 fortunately 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://aluigi.org/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://aluigi.org/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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