Pico Server (pServ) Local Information Disclosure
RedTeam found a local information disclosure vulnerability in Pico Server (pServ) which results in a local user reading all files on the server with pServ's permissions.
Product: Pico Server (pServ)
Affected Version: 3.3, 3.2(verified), < 3.2 probably too
Immune Version: none
OS affected: all
Pico Server is a small web server. It is meant to be portable and configurable.
* small, portable
* 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 follows symlinks without checking whether a symlink points outside the webroot.
pServ does not distinguish normal files from symlinks. Unfortunately it does furthermore only check the link itself but not check if the symlink target is still in the webroot. That is why an attacker with access to a directory on the web server (e.g. via ftp) can put a symlink to any file on the server there. He can then retrieve that file (if pServe has the permission to read it) through the web server by navigating his browser to that link.
Proof of Concept
Retrieving /etc/shadow if pServe runs as root:
1. As user go to your web-directory e.g.: cd /usr/local/var/www/userdir
2. Create a link to /etc/shadow: ln -s /etc/shadow
3. Retrieve the shadow file by pointing your browser to http://vuln-host:2000/userdir/shadow
pServe should run as a user with minimal privileges. Files that should not be read by unprivileged users should have their permissions set accordingly.
The problem will not be fixed in the next version of pServ. From version 3.3 on there is a hint in the readme file that informs of this issue.
The security risk is rated low because an attacker must already have access to the system. Also usually the administrator will run pServ with minimal privileges. On the other hand a user could place a link to some directory (e.g.: / ) without knowing what he is doing.
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 got the information that the problem will not be fixed. Advisory
2009-05-08 Updated Advisory URL
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