Advisory: Pico Server (pServ) Information Disclosure Of CGI Sources

RedTeam found a Information Disclosure vulnerability in Pico Server (pServ)
which gives an attacker the ability to read all files from cgi-bin.

Details
=======

Product: Pico Server (pServ)
Affected Version: 3.2(verified), <=3.2 probably too
Immune Version: 3.3
OS affected: all
Security-Risk: medium
Remote-Exploit: yes
Vendor-URL: http://pserv.sourceforge.net/
Vendor-Status: new version available
Advisory-URL: http://tsyklon.informatik.rwth-aachen.de/redteam/rt-sa-2005-011
Advisory-Status: published
CVE: CAN-2005-1366
(http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-1366 #)


Introduction
============

>From http://pserv.sourceforge.net/
Pico Server is a small web server. It is meant to be portable and
configurable.

* small, portable
* fast
* CGI-BIN support
* auto-indexing of directories
* access and error logging (see p-reporter for an analyzer)
* forking or single-connection at choice

Pico Server (pServ) is written in portable C (K&R style so it can compile on
older compilers too) and sports several options that by means of #define
statements can customize the behavior, the performance and the feature set so
to be able to fit better the the requisites.

Pserv does not correctly check whether a user accesses a file in cgi-bin and
gives away the source instead of executing it.

More Details
============

pServ has CGI-BIN support. Only URLs beginning with "cgi-bin" are treated as
cgi-scripts.
pServ checks, whether a file is in cgi-bin by checking whether the beginning
of the directory part of the url matches "cgi-bin". A user can circumvent
this by asking for /somedir/../cgi-bin/ and therefore is able to retrieve the
complete sourcecode of all scripts in cgi-bin.

Proof of Concept
================

This url lets us download the source of test.pl instead of executing it.
http://vuln-host:2000/somedir/../cgi-bin/test.pl

Workaround
==========

n/a

Fix
===

The Developers have released Version 3.3. This version should fix the
problem. The changes have not been tested by RedTeam, yet.

Security Risk
=============

The security risk is rated medium because a remote attacker can get source
code that would otherwise not be available to him. This can help the attacker
in further attacks. As many programmers put sensitive configuration
parameters like database passwords in the source code this attack can be
quite harmful.

History
=======

2005-04-29 found
2005-05-02 first attempt to inform developers
2005-05-02 CAN-number assigned
2005-05-04 second attempt to inform developers
2005-05-16 new version released. Advisory published.

RedTeam
=======

RedTeam is a penetration testing group working at the Laboratory for
Dependable Distributed Systems at RWTH-Aachen University. You can find more
Information on the RedTeam Project at
http://tsyklon.informatik.rwth-aachen.de/redteam/