[NT] AVTronics InetServer DoS and Buffer Overflow Vulnerabilities

From: support@securiteam.com
Date: 08/24/01


From: support@securiteam.com
To: list@securiteam.com
Subject: [NT] AVTronics InetServer DoS and Buffer Overflow Vulnerabilities
Message-Id: <20010824141535.A9324138BF@mail.der-keiler.de>
Date: Fri, 24 Aug 2001 16:15:35 +0200 (CEST)

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  AVTronics InetServer DoS and Buffer Overflow Vulnerabilities
------------------------------------------------------------------------

SUMMARY

 <http://www.avtronics.net/> AVTronics InetServer is a freeware product
suite for MS Windows, bundling services such as SMTP, POP3, Daytime and
Telnet in one product.
Two security vulnerabilities in the product allow remote attacker to
overflow internal buffers, leading to a denial of service attack and
possibly arbitrary code execution.

DETAILS

Vulnerable systems:
InetServer version 3.2.1
InetServer version 3.1.1

Denial of Service
If the Webmail daemon receives a buffer of about 800 bytes or more, the
InetServer process will die. This could be abused to launch a Denial of
Service attack against the server.

WWW-Authentication buffer overflows
The second problem is similar to the DoS, and also applies to the Webmail
interface, but poses a more severe threat to the system since the contents
of the buffer is written over the EIP, which enables remote code
execution.

Typically, when a user intends to access his/her mailbox through the
Webmail interface, this is done through a URL constructed as follows:

http://server:port/username

Following a basic WWW-Authentication (where the Realm is 'username') the
user is then taken into the specified mailbox. The problem lies in the
handling of the information provided to the server by the browser during
this WWW-Authentication. In certain cases, the username and password
combined can compose a buffer to smash the EIP.

Example:
username: 140 byte username
password: 140 byte password

This will overflow the buffer, where the EIP is overwritten by the last 4
chars of the password buffer. The same goes for other combinations as say
for example a 700 byte username and a 20 byte password.

Since WWW-Authentication is triggered through any 'username' following the
location of the Webmail interface, no prior knowledge of existing
usernames is necessary to successfully complete this attack.

Solution:
Vendor has been notified. Currently we are not aware of any forthcoming
fixes.

ADDITIONAL INFORMATION

The information has been provided by <mailto:vuln-dev@greyhack.com> SNS
Research.

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