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A U S C E R T A L E R T
AL-2001.15 -- AUSCERT ALERT
W32/Nimda.A@mm worm
19 September 2001
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PROBLEM:
AusCERT has been made aware of the existence of a new mass mailing
worm "Nimda" that spreads itself in attachments named "readme.exe".
The execution of this file causes the infected host computer to begin
scanning for vulnerable implementations of Internet Information Server
(IIS). The worm does this by either scanning for a backdoor created by
Sadmind and CodeRed II worms, or the IIS unicode vulnerability.
We have received significant numbers of reports of infection by this
virus from Australian and New Zealand sites, indicating that it is
propagating rapidly.
The propagation Nimda performs via email appears to involve sending
copies of itself to all addresses listed in the infected machine's
Outlook address book. All messages sent appear to contain the
following string in the mime-encoding of the attachment:
Content-ID: <EA4DMGBP9p>
The worm appears to:
- contain the string "Concept Virus(CV) V.5, Copyright(C)2001
R.P.China"
- contain a base64 encoding of a file name 'readme.exe'
- rename or edit of wininit.ini
- share the C drive
- create a guest account and add that account to the Administrators
and Guests group
- perform the root.exe (Sadmind / CodeRed II) and unicode exploits
- mails a copy of itself as readme.exe
Due to a vulnerability described in ESB-2001.134 (CERT Advisory
CA-2001-06 - Automatic Execution of Embedded MIME Types), any
mail software running on an x86 platform that uses Microsoft
Internet Explorer 5.5 SP1 or earlier (except IE 5.01 SP2) to
render the HTML mail automatically runs the enclosed attachment
and, as result, infects the machine with the worm. Thus, in
vulnerable configurations, the worm payload will automatically be
triggered by simply opening (or previewing) this mail message.
As an executable binary, the payload can also be triggered by
simply running the attachment.
Organisations running web servers and IDS systems will see a large
increase in web-vulnerability scanning. This virus is scanning
for backdoors left in IIS web servers, possibly by the Code Red
II worm.
Details of the Sadmind and CodeRed worms and the IIS unicode
vulnerability can be found at:
Sadmind -
ftp://ftp.auscert.org.au/pub/auscert/advisory/AL-2001.08
CodeRed II -
ftp://ftp.auscert.org.au/pub/auscert/advisory/AL-2001.14
IIS unicode vulnerability -
ftp://ftp.auscert.org.au/pub/auscert/advisory/AL-2001.02
ftp://ftp.auscert.org.au/pub/auscert/ESB/ESB-2000.360
PLATFORM:
For the Unicode Bug, unpatched IIS 4.0 and 5.0 servers are
vulnerable to attacks from Nimda infected machines. IIS 4.0 and
5.0 servers that have been previously compromised, and are still
compromised, by Sadmind or CodeRedII are also vulnerable to
attacks.
Nimda is also a Win32 executable and poses a threat to Microsoft
Windows operating systems that run Win32 (32-bit) applications.
These systems include, but are not limited to Windows 95, 98, ME,
Windows NT4 and Windows 2000.
Nimda specifically propagates via any mail software running on an
x86 platform that uses Microsoft Internet Explorer 5.5 SP1 or
earlier (except IE 5.01 SP2) to render the HTML mail automatically.
IMPACT:
Nimda has the ability to degrade network and system performance
and possibly cause a denial of service. Systems infected with Nimda
are also susceptable to intruders executing arbitrary code in a Local
System context.
RECOMMENDATIONS:
A. Detection
To check if you have the Nimda virus, either use your virus scanner
with a recent update (check with your vendor to ensure the scanner
can detect Nimda), follow any instructions supplied by virus
scanner vendors (see the links below).
Organisations should consider blocking or quarantining .exe files
at the email gateway. This should prevent the Nimda virus
infecting computers not running vulnerable versions of IIS (eg
workstations), however it is recommended that all organisations
contact their anti-virus vendors for an updated virus signature
file that will detect this virus.
B. Recovery
If you detect Nimda on one machine, it is vital to check for the
presence of the virus on *all* potentially affected systems,
including systems connected via network shares to the infected
machine. This may be accomplished using a current version of an
anti-virus program that is certified by the vendor to detect them,
or following the recovery steps listed at the following sites:
http://vil.mcafee.com/dispVirus.asp?virus_k=99209
http://www.symantec.com/avcenter/venc/data/w32.nimda.a@mm.html
http://www.antivirus.com/vinfo/virusencyclo/default5.asp?VName=TROJ_NIMDA.A
http://www.sophos.com/virusinfo/analyses/w32nimdaa.html
http://www.f-secure.com/v-descs/nimda.shtml
C. User Education
System Administrators are urged to inform their users about proper
precautions with regards to handling email attachments.
AusCERT recommends that sites should update and check their virus
defences and either delete or quarantine any email messages or
attachments that resemble those described above or in the following
links.
D. Update Anti-Virus Packages
System administrators and users are urged to ensure that the latest
Anti-Virus software is installed and that it is using the most
current up-to-date virus databases.
More information can be found at:
http://vil.mcafee.com/dispVirus.asp?virus_k=99209
http://www.symantec.com/avcenter/venc/data/w32.nimda.a@mm.html
http://www.antivirus.com/vinfo/virusencyclo/default5.asp?VName=TROJ_NIMDA.A
http://www.sophos.com/virusinfo/analyses/w32nimdaa.html
http://www.f-secure.com/v-descs/nimda.shtml
E. Patch Vulnerable Versions of Windows Workstations
If you are running a vulnerable version of Internet Explorer (IE),
the CERT/CC recommends applying patch for the "Automatic
Execution of Embedded MIME Types" vulnerability available from
Microsoft per AusCERT Bulletin:
ftp://ftp.auscert.org.au/pub/auscert/ESB/ESB-2001.131
E. Patch Vulnerable Versions of IIS
Microsoft System Administrators are urged to check their systems
for insecure versions of IIS services as per AusCERT Alerts and
Bulletins available from:
Sadmind -
ftp://ftp.auscert.org.au/pub/auscert/advisory/AL-2001.08
CodeRed II -
ftp://ftp.auscert.org.au/pub/auscert/advisory/AL-2001.14
IIS unicode vulnerability -
ftp://ftp.auscert.org.au/pub/auscert/advisory/AL-2001.02
ftp://ftp.auscert.org.au/pub/auscert/ESB/ESB-2000.360
This alert is to also remind you about the recent release of a
software tool available from Microsoft to detect the presence or
absence of security patches on some Microsoft based operating
systems and applications.
Microsoft has released the following description: "The Hfnetchk
tool is a command-line tool that you can use to assess a computer
or selected group of computers for the presence or absence of
security patches. You can use Hfnetchk to assess patch status for
the Windows NT 4.0 and Windows 2000 operating systems, as well as
hotfixes for IIS 4.0, IIS 5.0, SQL Server 7.0, and SQL Server 2000
(including MSDE), and Internet Explorer 5.01 or later.
The Hfnetchk tool uses an Extensible Markup Language (XML) file
that contains information about which hotfixes are available for
which products. The XML file contains security bulletin name and
title, and detailed data about product-specific security hotfixes,
including: files in each hotfix package and their file versions
and checksums, registry keys that were applied by the hotfix
installation package, information about which patches supersede
which other patches, related Microsoft Knowledge Base article
numbers, and much more."
Additional information and download instructions are available from:
http://support.microsoft.com/support/kb/articles/q303/2/15.asp
Frequently Asked Questions about the Microsoft Network Security
Hotfix Checker Tool is available from:
http://support.microsoft.com/support/kb/articles/Q305/3/85.ASP
AusCERT is releasing this information to its members for their
information only. AusCERT does not endorse or recommend any
program or tool listed in this message. Members are encouraged
to review and verify all information before using any tool.
F. Check For Signs of Compromise
If you suspect that your site may have been compromised, we
encourage you to read:
ftp://ftp.auscert.org.au/pub/cert/tech_tips/intruder_detection_checklist
If your site has been compromised, we encourage you to read:
http://www.auscert.org.au/Information/Auscert_info/Papers/win-UNIX-system_compromise.html
AusCERT is currently monitoring this problem, if you detect your
systems have been compromised please contact AusCERT.
On a possibly related note, AusCERT has received reports indicating
an increase in unauthorised network scans across a range of TCP
and UDP ports. Members are encouraged to stay alert for any signs
of network traffic which may indicate the use of scanning tools
in an attempt to find already compromised servers.
These attacks are currently widespread and AusCERT is releasing
this information to alert system administrators to this activity.
Member sites may wish to check their systems for evidence of
attacker activity of malformed URL requests directed at IIS
servers.
AusCERT will continue to monitor the situation and we would
appreciate any reports regarding this activity. If you have any
information, comments or questions about this threat, please
contact us.
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The AusCERT team has made every effort to ensure that the information
contained in this document is accurate at the time of publication. However,
the decision to use the information described is the responsibility of
each user or organisation. The appropriateness of this document for an
organisation or individual system should be considered before application
in conjunction with local policies and procedures. AusCERT takes no
responsibility for the consequences of applying the contents of this
document.
If you believe that your system has been compromised, contact AusCERT or
your representative in FIRST (Forum of Incident Response and Security
Teams).
AusCERT maintains an anonymous FTP service which is found on:
ftp://ftp.auscert.org.au/pub/. This archive contains past SERT
and AusCERT Advisories, and other computer security information.
AusCERT maintains a World Wide Web service which is found on:
http://www.auscert.org.au/.
Internet Email: auscert@auscert.org.au
Facsimile: (07) 3365 7031
Telephone: (07) 3365 4417 (International: +61 7 3365 4417)
AusCERT personnel answer during Queensland business
hours which are GMT+10:00 (AEST). On call
after hours for emergencies.
Postal:
Australian Computer Emergency Response Team
The University of Queensland
Brisbane
Qld 4072
AUSTRALIA
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