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Home » Hacking News » Abyss 1.0.3 directory traversal and administration bugs

Abyss 1.0.3 directory traversal and administration bugs

by Nikola Strahija on August 22nd, 2002 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.


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 winntwin.ini file:

"GET /..........winntwin.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
This is for view winnt:

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:


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:

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:



3) The Code

A] Example of the directory traversal bug on Win:

"GET /..........winntwin.ini HTTP/1.0"

Abyss index on Linux:


B] For the administration bug watch the html file in my userpage

It can be used to test the server that run on the same machine, at
the address
If you want to test other machines simply replace the string
"" 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.


4) Fix

Abyss 1.0.3 (patch 3) from the Aprelium web-site:

or directly the updated executable:


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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