ENSRT Incident Note ETS-i-2005-12578

The Enterasys Networks Security Response Team (ENSRT) publishes incident notes to provide information for our constituents to raise awareness of issues deemed threatening to the security and integrity of our customers.

Worm - W32.Mytob.DG@mm

Release Date: 06/06/2005
Last Updated:

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Overview

W32.Mytob.DG@mm is a mass-mailing worm that gathers e-mail addresses from various files on the infected system and uses its own SMTP engine to proliferate. Additionally, the worm opens a backdoor connection to an IRC server using TCP port 4512 where it listens for further commands from a remote attacker.

Details below describe the characteristics of the W32.Mytob.DG@mm as well as provide detection, containment, and prevention techniques available through Enterasys Secure Networks solutions.

Systems affected

Windows operating systems

Systems not affected

Linux and MAC/OSX

Description

W32.Mytob.DG@mm arrives in a user mailbox with either a random subject or one of the following erroneous warnings:

- Notice: **Last Warning**
- *DETECTED* Online User Violation
- Your Email Account is Suspended For Security Reasons
- Account Alert
- Important Notification
- *WARNING* Your Email Account Will Be Closed
- Security measures
- Email Account Suspension
- Notice of account limitation

The e-mail message will consist of one of the following strings:

- Once you have completed the form in the attached file , your account records will not be interrupted and will continue as normal.
- The original message has been included as an attachment.
- We regret to inform you that your account has been suspended due to the violation of our site policy, more info is attached.
- We attached some important information regarding your account.
- Please read the attached document and follow it's instructions.

The e-mail contains an attached file with one of the following extensions:

- pif
- scr
- exe
- cmd
- bat
- zip

Once the attached file is executed, the system will become infected. The infection process consists of the following actions:

1) The worm renames itself as "We Love Lien Van de Kelder.exe" on the system directory of the infected machine.

2) The worm creates system registry entries in an attempt to ensure that it is executed each time the Windows Operating system is started. The worm will automatically recreate these registry entries if they are deleted.

3) The worm Gathers e-mail addresses from various system files and uses its own SMTP engine to send copies of itself to a modified list of gathered e-mail addresses.

4) The worm opens a backdoor listening port (TCP 4512) for the purpose of allowing a remote attacker to issue commands. Some of the actions that can be executed are the ability to download and execute files, obtain an updated version of the worm, and remove or update the worm.

5) The worm will alter the system hosts file in an attempt to block access to various security related web sites, and will also halt various security related processes.

Threat Assessment

Mass-mailing worms if not addressed through prudent remediation steps may congest mail servers and/or degrade network performance. Mass-mailing worms may impact individual system performance and compromise security settings allowing unauthorized remote access to the compromised host.

Trojans or backdoor listeners if not addressed through prudent remediation steps, can compromise network and host security. Additionally, trojans and backdoor listeners potentially allow theft of information, unauthorized remote access, and damage to critical files.

Remediation

Matrix N7	X
Matrix E7	X
Matrix E6	X
Matrix E5	X
Matrix E1	X
VH	X
C-Series	X

Detection

Alternative Dragon signatures to detect the W32.Mytob.DG@mm worm can be retrieved via Dragon Live Update and are located in the Master Library within the ENSRT category. The signatures "ENSRT:W32-MYDOOM-BO-001" and "ENSRT:WORM-MYTOB-AR-(001-004)" can be copied into a custom library. Deploying the above signatures on a Dragon network sensor that is protecting the enterprise SMTP server can successfully detect end-user class machines which have become infected with the worm.

If utilizing Dynamic Intrusion Response (DIR), a Dragon Alarmtool policy that consists of an event group that contains the above signatures should be used. A threshold parameter of at least three signature detections within a time span of 60 seconds should be used to mitigate the existence of false positives.

NOTE: All signatures in the ENSRT library are disabled by default. These signatures must be enabled after they are imported into a custom library if they are to be successfully deployed.

Prevention

Trusted End System solutions are capable of monitoring various end system activity. TES is able to take immediate action such as firewalling specific IPs, TCP/UDP ports, applications, or placing the user into a Quarantine policy or VLAN until end system threat is mitigated. Learn more at: http://www.enterasys.com/solutions/secure-networks/trusted_end_system/

Containment

The Enterasys Dynamic Intrusion Response (DIR) solution can be utilized to remove infected end-users from the enterprise network by detecting the infection with a Dragon NIDS signature (see "Detection" section of this report), locating the user's connection point using Automated Security Manager's location services module, and either placing the user in a quarantine VLAN or disabling the associated switch port for the user.

Using Enterasys Policy Manager, enforce a policy that allows SMTP traffic from end user PCs to authorized SMTP mail servers and blocks SMTP traffic to unauthorized end users or unknown Internet systems. If the SMTP protocol is not implemented for end users within the enterprise, consider implementing a policy blocking SMTP traffic from end user ports.

Internet or edge facing firewalls should be configured with a default 'Deny' policy and contain 'Permit' policies for only needed services and applications. Furthermore, careful inspection of firewall policies that allow TCP traffic streams to be initiated from the Internet into internal enterprise resources is required. These policies should only allow specific protocols to trusted servers thereby combating the increased use of random TCP ports by Internet Trojans and worms.

Repair

Monitor Dragon Realtime Console for alerts that end-user PCs have become infected with the virus. If utilizing the DIR solution, users can either be expunged from the network or placed in a quarantine VLAN. Once isolated, see your anti-virus vendor for Windows repair procedures for infected users.

Scan all clients and servers for newly opened TCP ports that did not appear in previous TCP scans. If viruses are detected apply appropriate removal tools on each client and server that have the open ports (See your anti-virus solution for removal instructions).

References

http://securityresponse.symantec.com/avcenter/venc/data/w32.mytob.dg@mm.html

This document and the information contained herein are intended solely for informational use. Enterasys Networks, Inc. makes no representations or warranties of any kind, whether expressed or implied, with respect to this information and assumes no responsibility for its accuracy or completeness. Enterasys Networks, Inc. hereby disclaims all liability and warranty for any information contained herein and all the material and information herein exists to be used only on an "as is" basis. More specific information may be available on request. By your review and/or use of the information contained herein, you expressly release Enterasys from any and all liability related in any way to this information.

A copy of the text of this section is an uncontrolled copy, and may lack important information or contain factual errors. All information herein is Copyright ©Enterasys Networks, Inc. All rights reserved. All information above is subject to change without notice.

Revision History:

Version: 1.0

Date: 06/06/2005

Author: ENSRT STAFF

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