PHPlist, http://www.phplist.com is a popular open source newsletter 
application written in PHP.

Recently a file injection vulnerability has been discovered allowing 
remote attackers to issue arbitrary commands on the hosted machine, as 
the webserver user.
The issue has been resolved in the latest release, version 2.6.4 
available at http://www.phplist.com/files

Versions affected: any version up to 2.6.2

If Apache is used, the following .htacces file in the "admin" directory 
will patch the problem for any affected version, provided the server 
permissions allow overriding the relevant directives

<FilesMatch "\.(php|inc)$">
Order allow,deny
deny from all
</FilesMatch>
<FilesMatch "index.php$">
Order allow,deny
allow from all
</FilesMatch>

Michiel Dethmers