CERT-In Incident Note CIIN-2003-02

W32/Blaster worm

Original Issue Date: August 16, 2003

Severity: High

Type: Worm

Strategies: Microsoft has published information about this vulnerability in Microsoft Security Bulletin MS03-026.

Systems Affected:

Microsoft Windows NT® 4.0
Microsoft Windows NT 4.0 Terminal Services Edition
Microsoft Windows 2000
Microsoft Windows XP
Microsoft Windows ServerT 2003

Overview

W32/Blaster worm is taking advantage of "Buffer Overrun In RPC Interface" causing Denial of Service. This worm has aliases viz. W32/Lovsan.worm, W32/Blaster-A, W32.Blaster.Worm, Worm.Win32.Lovesan WORM_MSBLAST.B [Trend], Win32.Poza.C [CA], W32/Lovsan.worm.c [McAfee], Worm.Win32.Lovesan [KAV]

Impact

• A remote attacker could exploit "RPC Buffer Overflow " vulnerability and execute arbitrary code with Local System privileges or to cause denial-of-service (DoS) condition
• The worm activate from 16th to end of the month, for the months, January to August and on all days from September to December.
• Performs Denial of Service against windowsupdate.com
• May cause machines to crash.
• Opens a hidden remote cmd.exe shell.

Description

The W32/Blaster worm exploits a vulnerability in Microsoft's DCOM RPC interface as described in CERT-In Advisory CIAD-2003-09. Upon successful execution, the worm attempts to retrieve a copy of the file msblast.exe from the compromising host. Once this file is retrieved, the compromised system then runs it and begins scanning for other vulnerable systems to compromise in the same manner. In the course of propagation, a TCP session to port 135 is used to execute the attack. However, access to TCP ports 139 and 445 may also provide attack pointers and should be considered when applying mitigation strategies. Microsoft has published information about this vulnerability in Microsoft Security Bulletin MS03-026.

The worm has the ability to launch a TCP SYN flood denial-of-service attack against windowsupdate.com. Sites that do not use windowsupdate.com to manage patches may wish to block outbound traffic to windowsupdate.com, this should be done by thoroughly understanding organization's network routing aspects.
The worm generates an IP address and attempts to infect the computer that has that address and sends data on TCP port 135, which may exploit the DCOM RPC vulnerability. The local subnet will become saturated with port 135 requests. Due to the random nature of how the worm constructs the exploit data, this may cause computers to crash if it sends incorrect data.

Symptoms

In most cases, an infection will be indicated by the presence of the registry key "HKEY_LOCAL_MACHINE\SOFTWARE \Microsoft \Windows\ CurrentVersion \ Run\windowsautoupdate" with a value of msblast.exe.

Presence of following files on the system:

. msblast.exe
. teekids.exe
. penis32.exe

Removal Instructions

To remove this worm follow the steps:
1. Physically disconnect the system from network.
2. Check the system for signs of compromise.
In most cases, an infection will be indicated by the presence of the registry key "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft \Windows\CurrentVersion \Run\ windows auto update" with a value of msblast.exe. If this key is present, remove it using a registry editor.
3. If the machine is infected, terminate the running copy of msblast.exe, teekids.exe or penis32.exe using the Task Manager.
4. Search for and delete files named msblast.exe, teekids.exe or penis32.exe
5. Reboot the system

Solution

Apply patches

All users are encouraged to apply the patches referred to in Microsoft Security Bulletin MS03-026 as soon as possible in order to mitigate the vulnerability. These patches are also available via Microsoft's Windows Update service.
Systems running Windows 2000 may still be vulnerable to at least a denial-of-service attack if their DCOM RPC service is available via the network. Therefore, sites are encouraged to use the packet filtering tips below in addition to applying the patches supplied in MS03-026.
It has been reported that some affected machines are not able to stay connected to the network long enough to download patches from Microsoft. For hosts in this situation, removal instructions mentioned above should be taken.

Disable DCOM

Depending on site requirements, user may wish to disable DCOM as described in MS03-026. Disabling DCOM will help protect against this vulnerability but may also cause undesirable side effects. Additional details on disabling DCOM and possible side effects are available in Microsoft Knowledge Base Article 825750.

Filter network traffic

Sites should consider blocking both inbound and outbound traffic to the below mentioned ports, depending on network requirements, at the host and network level. Microsoft's Internet Connection Firewall can be used to accomplish these goals.

. 69 UDP
. 135 TCP
. 135 UDP
. 139 TCP
. 139 UDP
. 445 TCP
. 445 UDP
. 593 TCP
. 4444 TCP

The current exploits for VU#568148 create a backdoor, which is in some cases 4444/TCP, blocking inbound TCP sessions to ports on which no legitimate services are provided may limit intruder access to compromised hosts.

Anti-virus vendors have also published steps to recover from mentioned worm infection, links are provided in references.

References

http://www.europe.f-secure.com/v-descs/msblast.shtml

http://www.trendmicro.com/vinfo/virusencyclo/default5.asp?
VName=WORM_MSBLAST.A

http://securityresponse.symantec.com/avcenter/venc/data/
w32.blaster.b.worm.html

http://support.centralcommand.com/cgi
in/command.cfg/php/enduser/std_adp.php?p_faqid=506

CERT-In Advisory CIAD-2003-09
http://www.cert-in.org.in/advisory/ciad-2003-09.htm

CERT/CC Advisory CA-2003-20
http://www.cert.org/advisories/CA-2003-20.html

CERT/CC W/32 Blaster Recovery Tips:
http://www.cert.org/tech_tips/w32_blaster.html
http://www.kb.cert.org/vuls/id/568148
http://www.kb.cert.org/vuls/id/326746

Microsoft Security Bulletin MS03-026
http://microsoft.com/technet/security/bulletin/MS03-026.asp

Microsoft Knowledge Base article 823980
http://support.microsoft.com?kbid=823980

Disclaimer
The information provided here-in is on "as is" basis, without warranty of any kind.

Postal address:
Indian Computer Emergency Response Team (CERT-In)
Ministry of Communications and Information Technology
Electronics Niketan
6, C.G.O. Complex
New Delhi-110 003