ENSRT Incident Note ETS-i-2005-12574

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.Stubbot.A@mm

Release Date: 05/19/2005
Last Updated:

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Overview

W32.Stubbot.A@mm is a mass-mailing worm that retrieves e-mail addresses from files located on the infected computer and uses an embedded SMTP engine to further proliferate. Additionally, the worm also opens an IRC back door on TCP port 6677 as well as attempts to spread through weak network shares.

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

Systems affected

Systems not affected

Description

The W32.Stubbot.A@mm mass mailer arrives on the user's PC via an e-mail with an enclosed attachment. The e-mail subject line will contain one of the following:

- Mail Deliviry Failure
- Mail Encoded
- Mail Authentification
- Message Error
- Protected Mail Delivery
- Hello there :)

The e-mail will include one of the following bodies:

- Your mail couldnt be delivered, please check the attachment for info
- Mail is encoded, check attachment for decrypted mail
- You have received an extended message. Please read the instructions. New message is available
- Follow the instructions to read the message
- SMTP: Please confirm the attached message.
- Protected message is attached.
- Check what i found. Its save in PIF format (Picture image Format)
- Sexy screensaver for You, delivered by a friend.
- Someone sent you a sexy screensaver.

The e-mail will also contain one of the following attachments.
- svthx.exe
- Test
- Test.exe
- Test.pif
- Test.zip
- haha.pif
- haha.zip
- Details.pif
- Details.zip
- Decrypted_mail.pif
- Decrypted_mail.zip
- Instructions-howtofix.txt.pif
- Instructions-howtofix.txt.zip
- Protected.Storage.Encrypted.XOR.34h.pif
- Protected.Storage.Encrypted.XOR.34h.zip

If the attached executable is launched, the PC will become infected and the W32.Stubbot.A@mm worm will drop a copy of itself into the Windows system folder as "svthx.exe" and edit the system registry so that the worm is run at Windows system startup. In addition, the W32.Stubbot.A@mm worm opens a back door by connecting to an IRC channel on the "irc.ircme.net" domain using TCP port 6677. This allows a remote attacker to download and execute files, steal system information, terminate processes, log key strokes, or perform a host of other IRC commands.

The W32.Stubbot.A@mm worm then gathers e-mail addresses from files on the infected system and further proliferates with the aid of an embedded SMTP engine.

The W32.Stubbot.A@mm may also spread via P2P file-sharing networks using one of the following filenames:

- MSNPasswordStealer_Setup.exe
- MSNHack.exe
- AOL_Hack.exe
- AOL_Password_Stealer.exe
- mIRC 7.0 Beta.exe
- Setup.exe
- MSNBot_Setup.exe
- Winamp5.7Beta.exe
- MSN7Beta.exe
- ICQ2005.EXE

Lastly, the worm may attempt to spread through weak file shares by using an embedded list of commonly used passwords.

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

Detection

Specific Dragon signatures that detect the W32.Stubbot.A@mm worm can be retrieved via Dragon Live Update and are located in the Master Library within the ENSRT category. The seven signatures with the prefix "ENSRT:W32-STUBBOT-A" can be copied into a custom library and deployed on a Dragon network sensor that is protecting the enterprise SMTP server to 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 all of the signatures within the "ENSRT:W32-Stubbot-A" 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.

References

http://securityresponse.symantec.com/avcenter/venc/data/w32.stubbot.a@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: 05/19/2005

Author: ENSRT STAFF

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