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Targeted Trojan Email Attacks
Original release date: July 08, 2005
Last revised: --
Source: US-CERT
Overview
The United States Computer Emergency Readiness Team (US-CERT) has
received reports of an email based technique for spreading trojan
horse programs. A trojan horse is an attack method by which malicious
or harmful code is contained inside apparently harmless files. Once
opened, the malicious code can collect unauthorized information that
can be exploited for various purposes, or permit computers to be used
surreptitiously for other malicious activity. The emails are sent to
specific individuals rather than the random distributions associated
with a phishing attack or other trojan activity. (Phishing is the act
of sending an email to a user falsely claiming to be an established
legitimate enterprise in an attempt to scam the user into surrendering
private information that can be used for identity theft.) These
attacks appear to target US information for exfiltration. This alert
seeks to raise awareness of this kind of attack, highlight the
important need for government and critical infrastructure systems
owners and operators to take appropriate measures to protect their
data, and provide guidance on proper protective measures.
Description
There are two distinct elements that make this attack technique
significant. First, the trojans can elude conventional protective
measures such as anti-virus software and firewalls, both key measures
in protecting the US Critical Infrastructure networks. A number of
open source and tailored trojans, altered to avoid anti-virus
detection, have been used. Trojan capabilities suggest that
exfiltration of data is a fundamental goal. Second, the emails are
sent to specific or targeted recipients. Unlike "phishing" attacks,
the emails use social engineering to appear credible, with subject
lines often referring to work or other subjects that the recipient
would find relevant. The emails containing the trojanized attachments,
or links to websites hosting trojanized files are spoofed, making it
appear to come from a colleague or reliable party. The email
attachments exploit known vulnerabilities to install a trojan on the
user's computer. When opened, the file or link installs the trojan.
Trojans can be configured to transmit information to a remote attacker
using ports assigned to a common service (e.g., TCP port 80, which is
assigned to Web traffic) and thereby defeat firewalls. Once the
trojanized attachment is opened, a remote attacker can then perform
the following functions:
* Collection of usernames and passwords for email accounts
* Collection of critical system information and scanning of network
drives
* Use of infected machine to compromise other machines and networks
* Downloading of further programs (e.g., worms, more advanced
trojans)
* Uploading of documents and data to a remote computer
US-CERT is working with other computer emergency response teams
worldwide to address these types of attacks.
Suggested Actions
Due to the targeted distribution of trojans spread in this way and the
possibility of communication with remote attackers using ports
assigned to common services, detection of this activity is
problematic. US-CERT advises that system administrators take the
following actions:
* Educate users to use an anti-virus scanner on all email
attachments.
* Maintain and update anti-virus software and signatures to detect
malware that may be associated with this attack.
* Block executable and/or suspect attachment types at email gateway
or block the download of executable content via HTTP.
* Investigate anomalous slow-running machines, looking for unknown
processes or unexpected Internet connections, as this may be an
indication of malicious programs operating in the background.
Encourage reporting and full investigation of such behavior.
* Update operating system and application software to patch
vulnerabilities exploited in the past by these Trojans.
* Implement spam filtering to guard against infrastructures (e.g.,
dial-ups, open proxies and open relays) commonly used by the
attackers.
* As Microsoft Office vulnerabilities have been targeted and
exploited, ensure that Microsoft security bulletins are followed.
Microsoft Security Bulletins Search
http://www.microsoft.com/technet/security/current.aspx
* Turn off 'Preview Pane' functionality in email clients and set the
default options to view opened emails as plain text
* Examine firewall logs of critical systems, or networks used for
processing sensitive information, for connections to or from
anomalous IP addresses.
* Consider traffic analysis to identify any compromised computers
that are exfiltrating files. Data on the size and times of HTTP
transactions or TCP port 80 flows may help detect exfiltration by
highlighting connections where the data volume sent is far greater
than that received from the remote server or when data is being
sent at times outside of normal working hours.
* Analyze log files to determine whether the attackers are spoofing
your domain.
* Consider implementing IP address lists of outbound Internet
connections, denying access except from address ranges relevant to
your business activities, such as a "default deny" policy. This
provides some protection against computers in third countries
being used by attackers to control trojans.
Incidents or suspected malicious activity of this nature, as well as
all cyber security incidents affecting the US Critical Infrastructure
should be reported to the United States Computer Emergency Readiness
Team (US-CERT) via email to soc@xxxxxxxxxxx or by telephone (703)
235-5110.
Vendor Product Names
The following anti-virus product names are associated with known
trojans used in the attacks since January 2005.
McAfee
<http://www.mcafee.com>
* Backdoor-BCB
* BackDoor-CPY!chm
* Backdoor-TW
* Downloader-WY
* Exploit-1Table
* JS/BackDoor-CPY
* MultiDropper-MR
* Proxy-Sysgam
* Pusno
* StartPage-DH.dll
Sophos
<http://www.sophos.com>
* Troj/Agent-BX
* Troj/Agent-T
* Troj/DDrop-A
* Troj/Dloader-KF
* Troj/Dloader-KZ
* Troj/Lecna-C
* Troj/Nethief-M
* Troj/Nethief-N
* Troj/Nethief-O
* Troj/Netter-A
* Troj/Riler-E
* Troj/Riler-F
* Troj/Riler-J
* Troj/RPE-A
* Troj/Sharp-F
* Troj/VBDrop-A
* WM97/Loof-D
Symantec
<http://www.symantec.com>
* Trojan.Dropper
* Trojan.Mdropper.B
* Trojan.Riler.C
Trend Micro
<http://www.trendmicro.com>
* BKDR_NETHIEF.L
* BKDR_NETHIEF.R
* BKDR_NETHIEF.S
* BKDR_TUIMER.A
* TROJ_AGENT.KZ
* TROJ_SHARP.C
* TROJ_WINBLUE.A
* W2KM_PASSPRO.A
* W2KM_PASSPRO.C
* W2KM_PASSPRO.E
_________________________________________________________________
Feedback can be directed to US-CERT at soc@xxxxxxxxxxx
_________________________________________________________________
Produced 2005 by US-CERT, a government organization.
This document is available online.
<http://www.us-cert.gov/cas/techalerts/TA05-189A.html>
Terms of use
<http://www.us-cert.gov/legal.html>
Revision History
July 08, 2005: Initial release
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