FortiGuard Advisory (FGA-2006-18)

Fortinet advises that a recently discovered SMTP Sendmail email vulnerability was found and published by CERT. The Fortinet Engineering team has reviewed it and provided a fix for it. (CERT/CVE Reference: CVE-2006-1173)

We have received a report of a vulnerability in Sendmail caused by the way Sendmail handles multipart MIME messages. The impact of this vulnerability is a denial-of-service condition.

MIME messages can be composed of multiple parts (for example, a text portion and an HTML portion, or a text portion and an attached PDF or image file) and are commonly known as multipart messages. Each of these parts can contain multiple parts as well. It is possible to create MIME multipart messages which are deeply nested, i.e. a part within a part, within a part, etc.

During message delivery, these deeply nested MIME messages can exhaust the per-process stack space memory available and cause that process to abort. Depending on system configuration, this may also cause a core dump for that process to be written to disk.

To the best of our knowledge, this type of attack is not currently in use and the problem was found through a report of an isolated and unintentional incident. That said, the information contained in this advisory is now generally known and there may be a higher likelihood of occurrence. Therefore, Sendmail recommends that you take immediate action with patches or workarounds.

Fortinet's Analysis:

It turns out that the problem is caused by malformed multipart messages not the nesting level. Specifically, if a message contains multiple MIME parts that are malformed in a certain way, this vulnerability will be triggered. All other information from the original Sendmail Advisory remains unchanged. According to Sendmail, the patches and workarounds from the original advisory will still adequately correct this problem.

Products affected:

All FortiMail models running software prior to version 2.8 build 083.

Risk:

Low, the process which exits abnormally is not the server process and will not cause your system to stop accepting connections.

Solution:

A fix for the Sendmail issue has been provided in FortiMail version 2.8 build 083 or higher. Contact Fortinet Tech Support to obtain firmware.

Disclaimer:

Although Fortinet has attempted to provide accurate information in these materials, Fortinet assumes no legal responsibility for the accuracy or completeness of the information. More specific information is available on request from Fortinet. Please note that Fortinet's product information does not constitute or contain any guarantee, warranty or legally binding representation, unless expressly identified as such in a duly signed writing.

About Fortinet ( www.fortinet.com ):

Fortinet is the pioneer and leading provider of ASIC-accelerated unified threat management, or UTM, security systems, which are used by enterprises and service providers to increase their security while reducing total operating costs. Fortinet solutions were built from the ground up to integrate multiple levels of security protection--including firewall, antivirus, intrusion prevention, VPN, spyware prevention and anti-spam -- designed to help customers protect against network and content level threats. Leveraging a custom ASIC and unified interface, Fortinet solutions offer advanced security functionality that scales from remote office to chassis-based solutions with integrated management and reporting. Fortinet solutions have won multiple awards around the world and are the only security products that are certified in six programs by ICSA Labs: (Firewall, Antivirus, IPSec, SSL, Network IPS, and Anti-Spyware). Fortinet is privately held and based in Sunnyvale, California.