(SRADV00005) Remote command execution vulnerabilities in MailMan Webmail

[Secure Reality Advisories <create () SECUREREALITY COM AU>]

=================================================
Secure Reality Pty Ltd. Security Advisory #5 (SRADV00005)
http://www.securereality.com.au
=================================================

[Title]
Remote command execution vulnerabilities in MailMan Webmail

[Released]
6/11/2000

[Vulnerable]
All 3.x versions of MailMan Webmail below 3.0.26

[Overview]
MailMan is a product by Endymion corporation that provides a web based
interface to email via POP3 and SMTP. MailMan is very popular due to its
amazingly easy setup and operation.

MailMan is written as a Perl CGI script, the version which is shipped to
customers is obfuscated in an attempt to prevent piracy. The code contains
several insecure calls to open() containing user specified data. These calls
can be used to execute commands on the remote server with the permissions of
the user that runs CGI scripts, usually the web server user which is in most
cases 'nobody'.

[Impact]
Remote command execution (with privileges as above)

[Detail]
MailMan uses template files to define the appearance of the output so that
customers can brand the software to their particular service (e.g ISP,
Educational Institution).

In previous versions of MailMan the location of the template files was
static. Versions above 3 developed the ability to have multiple different
sets of template files. The location of the template files is defined by a
form variable called 'ALTERNATE_TEMPLATES'. When opening the alternate
templates MailMan fails to specify the '<' operator to the infamous Perl
open() statement, it then executes an open which looks like the following:

open("$ALTERNATE_TEMPLATES_<action>.html");

Where <action> is a defined template name. Obviously since we have control
of the $ALTERNATE_TEMPLATES variable we easily use pipe redirection to
execute commands on the remote server. The following request will execute
"id" on a vulnerable remote web server and return the output to the browser:

/mmstdod.cgi?ALTERNATE_TEMPLATES=|%20echo%20"Content-Type:%20text%2Fhtml"%3B
echo%20""%20%3B%20id%00

Please note that if $mailman::strLocalTemplateLocation is defined in the
configuration section at the top of the script (it is commented out by
default and is rarely enabled) this attack will fail since we won't be able
to effect the beginning of the open string.

[Fix]
Please upgrade to the latest version of MailMan (3.0.26) at
http://www.endymion.com/products/mailman/download.htm
(Please note all references on the web page indicate the latest version is
3.0.25 as they have not yet been updated, the version downloadable from the
download page _is_ 3.0.26 as can be verified in the comments at the top of
the script)

[Acknowledgements]
Our thanks to Ryan Porter of Endymion Corporation for his extremely
cooperative response to this problem.

[Disclaimer]
Advice, directions and instructions on security vulnerabilities in this
advisory do not constitute: an endorsement of illegal behavior; a guarantee
that protection measures will work; an endorsement of any product or
solution or recommendations on behalf of Secure Reality Pty Ltd. Content is
provided as is and Secure Reality Pty Ltd does not accept responsibility for
any damage or injury caused as a result of its use.