full-disclosure - Medium security hole affecting W3Mail

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Message-ID: <200207251243.g6PChSII004087@firewall.home>
From: netsys at machine.org.uk (Tim Brown)
Subject: Medium security hole affecting W3Mail

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I believe I've found a medium level security hole relating to the way W3Mail
stores MIME attachments. ?I contacted the authors (CascadeSoft -
<http://www.cascadesoft.com/>) on the 19th, offering them 14 days to produce
a fix, but have had no reply to acknowledge that the problem even exists,
I've decided to publish this warning:

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Nth Dimension Security Advisory (NDSA20020719)
Date: 19th July 2002
Author: Tim Brown <mailto:timb@...-dimension.org.uk>
URL: <http://www.nth-dimension.org.uk/> / <http://www.machine.org.uk/>
Product: W3Mail (up to and including 1.0.5) <http://www.w3mail.org/>
Vendor: CascadeSoft <http://www.cascadesoft.com/>
Risk: Medium

Summary

This vulnerability come in 2 related parts.

1) W3Mail can incorrectly expose downloaded MIME attachments without
correct authentication in cases where the Web Server has been
configure with indexing for the MIME attachments storage directory.

2) In cases where the web server has server side scripting of any type
(such as PHP) enabled for the MIME attachments directory, it is
possible to gain remote access as the webserver user typically nobody.

Technical Details

1) Unless indexing for the MIME attachments directory is disabled it
is possible to browse the MIME attachments directory and read
arbitrary attachments.  Prior to release 1.0.3, W3Mail did not
correctly clean up the MIME directory, leaving the attachments there
even after the user whom they belonged to has logged out. In versions
1.0.3 and more recent, providing the user correctly logs out their
attachments will be removed. Note that the attachments will remain as
with 1.0.3 and lower releases if the user simply closes the window
rather than using the correct logout link.

2) By sending a MIME attachment executable by the web server from the
MIME attachments directory to an POP3 account accessed from the W3Mail
web based POP3 client remote access as the webserver user can in
theory be achieved, if the user to whom the mail is sent opens the
malicious email (and thus creates the attachments within the MIME
attachments directory for the lifetime explained in part 1).  Whilst
the attachment exists, the potential intruder can request it via their
browser and therefore have it exected by the web server.  The
attachment must be sent as a none text MIME type in order for the
malicious code to correctly be created. This part of the vulnerability
will work even when directory indexing is turned off for the MIME
attachments directory since attachments are created with their
original name.

This vulnerability can also be exploited on attachments being sent
from W3Mail, although in this case the affect is reduced in versions
from 1.0.3 onwards which clean the attachments directory after the
mail has been sent minimizing the potential time for any attack.

Solutions

In order to completely protect against the vulnerability (in the short
term), Nth Dimension recommend turning off indexing and any server
side file execution for the MIME attachments directory, however it is
our belief that it would be better to rewrite the affected code with a
view to storing attachments (either those being sent or received)
outside the web servers document root.
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I found it purely by chance, as one of my friends has a web stats utility
running on his W3Mail server - it was listing attachments, and I was
surprised to find that they could be accessed without any authentication -
more shocking still its possible to use this knowledge to upload malicious
code to be executed via a browser.

Cheers,
Tim
- --
Tim Brown
<mailto:netsys@...hine.org.uk>
<http://www.machine.org.uk/>

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