ENSRT Incident Note ETS-i-2005-12545
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.
Worms - W32.MyTob@mm - Variants Q, R, S
Release Date: 03/28/2005
Last Updated:
Overview
W32.MyTob@mm is a mass-mailing worm family that retrieves e-mail addresses from the Windows Address Book on the infected computer and uses an embedded SMTP engine to further proliferate the worm.
Details below will describe the characteristics of the W32.MyTob@mm worm family as well as provide detection, containment, and prevention techniques available through Enterasys Secure Networks solutions.
Systems affected
Windows operating systemsSystems not affected
Linux and MAC/OSXDescription
The W32.MyTob@mm worms arrive via e-mail attachments in the user's mailbox with the following characteristics:
Subject Line: The subject lines in all variants of the worm are innocuous one or two word combinations that tempt the end-user to open the e-mail document. Example subject lines include, "Error", "Server Report", and "Good Day". In addition, the subject line may consist of a blank field or random data.
Message Body: One of five possible message bodies are used to proliferate the worm. They are as follows:
- "The message cannot be represented in 7-bit ASCII encoding and has been sent as a binary attachment."
- "Mail transaction failed. Partial message is available."
- "The message contains Unicode characters and has been sent as a binary attachment."
- "Here are your banks documents."
- "The original message was included as an attachment."
Additionally, as with the subject line, the message body can be both blank or contain random data.
If a W32.MyTob@mm worm is executed on the host machine, it will infect the machine and begin the propagation process.
This process consists of the following actions:
1) The worm plants a copy of itself in the system folder of the infected machine.
2) The worm alters the system registry in order to insure that the worm runs at Windows system startup.
3) The worm gathers addresses from the host computer's address book files and, using its own SMTP engine, sends infected e-mail to the gathered list of addresses in hopes of further propagation.
4) The worm starts up an FTP server session on the host computer using a random port.
5) The worm opens an IRC session to an IRC server and waits for remote instructions from an attacker.
6) The worm attempts to scan for remote computers and try to exploit the Microsoft Windows Local Security Authority Service Remote Buffer Overflow
7) Blocks access to multiple security related websites, though specific host file modification.
-VARIANT R ONLY-
8) The worm attempts to invade network shared folders that are protected by weak passwords. If successful it will drop a copy of the virus in the folder.
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
A specific set of Dragon signatures that detect the W32.MyTob@mm worm family can be retrieved via Dragon Live Update and are located in the Master Library within the ENSRT category. The five individual signatures with the prefix "ENSRT:W32-MYTOB" can be copied into a custom library and deployed on a Dragon network sensor that is protecting the enterprise SMTP server. NOTE: The first three signatures also exist in previous ENSRT signature groups related to MyDoom variants. These five signatures were originally created to protect against previous W32.Mytob@mm worm variants and will additionally protect against these three variants as well.
If utilizing Dynamic Intrusion Response (DIR), a Dragon Alarmtool policy that consists of an event group that contains all of the signatures within the "ENSRT:W32-MYTOB" family 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.
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.q@mm.html
http://securityresponse.symantec.com/avcenter/venc/data/w32.mytob.r@mm.html
http://securityresponse.symantec.com/avcenter/venc/data/w32.mytob.s@mm.html
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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:
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Version: 1.0 |
Date: 03/28/2005 |
Author: ENSRT STAFF |
Change |