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                         Luigi Auriemma

Application: Abyss webserver
http://www.aprelium.com
Versions: minors than 1.2
Platforms: Linux version only
Bug: Bypassing of password protected folders authorization on
FAT32 filesystems
Risk: medium
(but rarely users use Linux to run a webserver on a FAT32
partition)
Exploitation: remote through browser
Date: 08 Dec 2003
Author: Luigi Auriemma
e-mail: [email protected]
web: http://aluigi.altervista.org

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

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1) Introduction

Abyss webserver is a nice and tiny free closed-source web server
developed for Win32, Linux x86, MacOS and FreeBSD platforms.

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2) Bug

The bug is a protection bypassing but it happens only on Linux when the
protected folder is on a FAT32 system. Probably is a bit unusual that
someone uses a webserver for Linux to share a FAT32 directory but Abyss
is very useful for fast configurations and for personal usages so
this is not a rare case (… in fact I have found this bug just because
I was sharing a FAT32 dir…).

Practically if the admin runs Abyss webserver on Linux and has a FAT32
directory protected by password an attacker can bypass the
authorization simply adding a dot or an HTTP encoded dot (%2e) at the
end of the URL.

The developers have reported that also the chars space (' ', %20) and
':' (%3a) cause the same problem (but on my system they cause only a
right 404 error).

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3) The Code

http://linux_server/protected_FAT32_dir.
http://linux_server/protected_FAT32_dir./
http://linux_server/protected_FAT32_dir%2e

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4) Fix

Version 1.2 released the 3th Dec 2003

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Luigi Auriemma
http://aluigi.altervista.org