What
is the MSBLAST.F?
Also known as: Blaster.F.Worm, W32/Lovsan.worm.f,
W32/Blaster-F, WORM_MSBLAST.G,
Win32.Poza.F
Blaster.F is a worm that exploits the DCOM RPC
vulnerability (described in Microsoft Security
Bulletin MS03-026) using TCP port 135. The worm
targets only Windows 2000 and Windows XP
computers. While Windows NT and Windows 2003
Servers are vulnerable to this exploit (if not
properly patched), the worm is not coded to
replicate to those systems. This worm attempts to
download the Enbiei.exe file into the %Windir%\System32
folder, and then execute it.
Blaster.F does not have a mass-mailing
functionality.
We recommend that you block access to TCP port
4444 at the firewall level, and then block the
following ports, if you do not use the following
applications:
- TCP Port 135, "DCOM RPC"
- UDP Port 69, "TFTP"
The worm also attempts to perform a Denial of
Service (DoS) on tuiasi.ro. At the time of
writing this description, tuiasi.ro resolves to a
blank address.
How
Does MSBLAST.F Worm Infect My System?
When it is executed, MSBLAST.F performs the
following actions:
- Checks to see whether a computer is already
infected and whether the worm is running. If
so, the worm will not infect the computer a
second time.
- Adds the value:
"www.hidro.4t.com"="enbiei.exe"
to the registry key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
so that the worm runs when you start
Windows.
- Generates an IP address and attempts to
infect the computer that has that address. The
IP address is generated according to the
following algorithms:
- For 40% of the time, the generated IP
address is of the form A.B.C.0, where A
and B are equal to the first two parts of
the infected computer's IP address.
C is also calculated by the third part of
the infected system's IP address; however,
for 40% of the time the worm checks
whether C is greater than 20. If so, a
random value less than 20 is subtracted
from C. Once the IP address is calculated,
the worm will attempt to find and exploit
a computer with the IP address A.B.C.0.
The worm will then increment the 0 part of
the IP address by 1, attempting to find
and exploit other computers based on the
new IP address, until it reaches 254.
- With a probability of 60%, the generated
IP address is completely random.
- Sends data on TCP port 135 that may exploit
the DCOM RPC vulnerability. The worm sends one
of two types of data: either to exploit
Windows XP or Windows 2000.
For 80% of the time, Windows XP data will be
sent; and for 20% of the time, the Windows
2000 data will be sent.
NOTES:
- The local subnet will become saturated
with port 135 requests.
- While W32.Blaster.F.Worm cannot spread
to the Windows NT or Windows Server 2003,
unpatched computers running these
operating systems may crash as a result of
the worm's attempts to exploit them.
However, if the worm is manually placed
and executed on a computer running these
operating systems, it can run and spread.
- Due to the random nature of how the worm
constructs the exploit data, this may
cause the RPC service to crash if it
receives incorrect data. This may manifest
as svchost.exe, generating errors as a
result of the incorrect data.
- If the RPC service crashes, the default
procedure under Windows XP and Windows
Server 2003 is to restart the computer. To
disable this feature, see step one of the
"Removal Instructions" below.
- Uses Cmd.exe to create a hidden remote shell
process that will listen on TCP port 4444,
allowing an attacker to issue remote commands
on an infected system.
- Listens on UDP port 69. When the worm
receives a request from a computer to which it
was able to connect using the DCOM RPC
exploit, it sends Enbiei.exe to that computer
and tells it to execute the worm.
- If the current date is the 16th through the
end of the month for the months of January to
August, or if the current month is September
through December, the worm will attempt to
perform a DoS on tuiasi.ro. However, the
attempt to perform the DoS will succeed only
if one the following conditions is true:
- The worm runs on a Windows XP computer
that was either infected or restarted
during the payload period.
- The worm runs on a Windows 2000 computer
that was infected during the payload
period and has not been restarted since it
was infected.
- The worm runs on a Windows 2000 computer
that has been restarted since it was
infected, during the payload period, and
the currently logged in user is
Administrator.
- The DoS traffic has the following
characteristics:
- Is a SYN flood on port 80 of tuiasi.ro.
- Tries to send 50 HTTP packets every
second.
- Each packet is 40 bytes in length.
- If the worm cannot find a DNS entry for
tuiasi.ro, it uses a destination address
of 255.255.255.255.
Some fixed characteristics of the TCP and IP
headers are:
- IP identification = 256
- Time to Live = 128
- Source IP address = a.b.x.y, where a.b
are from the host ip and x.y are random.
In some cases, a.b are random.
- Destination IP address = dns resolution
of "tuiasi.ro"
- TCP Source port is between 1000 and 1999
- TCP Destination port = 80
- TCP Sequence number always has the two
low bytes set to 0; the two high bytes are
random.
- TCP Window size = 16384
Mitigating the DoS Payload
Network administrators can use the following
recommendations to mitigate the DoS payload:
- Reroute windowsupdate.com to a special
internal IP address: This will alert you to
the infected machines if you have a server
listening to catch the SYN flood.
- Configure anti-spoofing rules on the
routers, if this has not already been
implemented: This action will prevent a high
percentage of packets from leaving the
network. Using uRPF or egress ACLs would be
effective.
How to Remove the MSBLAST.F worm?
Kaspersky Internet Security Can Prevent You From Virus and Intrusion.
If Kaspersky detects MSBLAST.F during the
scan, it will AUTOMATICALLY offer you the option
of deleting it. Do this by following the
program's instructions.
Follow these steps
in removing the MSBLAST.F worm.
1. Applying Patches
Apply the patches issued by Microsoft from the
following page: Microsoft
Security Bulletin MS03-026
2. Disabling System Restore (Windows Me/XP)
For instructions on how to turn off System
Restore, read your Windows documentation, or one
of the following articles: "How
to disable or enable Windows Me/XP System Restore".
3. Updating the Virus Definitions
If you do not know which anti-virus software
can provide strong protection for you, Kaspersky Internet Security is recommended.
4. Ending the Worm process
- Press Ctrl+Alt+Delete once.
- Click Task Manager.
- Click the Processes tab.
- Double-click the Image Name column header to
alphabetically sort the processes.
- Scroll through the list and look for
Enbiei.exe.
- If you find the file, click it, and then
click End Process.
- Exit the Task Manager.
5. Scanning for and deleting the infected
files
- Start your Kaspersky Internet Security and make sure that it is
configured to scan all the files.
- Run a full system scan.
- If any files are detected as infected with
Blaster.F,
click Delete.
6. Reversing the changes made to the registry
- Click Start, and then click Run. (The Run
dialog box appears.)
- Type regedit
Then click OK. (The Registry Editor opens.)
- Navigate to the key:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
- In the right pane, delete the value:
"www.hidro.4t.com"="enbiei.exe"
- Exit the Registry Editor
How to Disinfect My Computer from Worms?
In order to keep your computer protected, bear
the following tips in mind:
- If you have filtering tools installed,
configure them to reject messages with the
characteristics described above. If, in spite
of doing this, you receive the message that
contains the virus: do not open it, do not run
the attached file and delete it, making sure
that you also delete it from the Deleted
Items folder.
- Install a good antivirus in your computer.
Select Kaspersky Internet Security to get the Kaspersky antivirus solution that best suits your needs.
- Keep your antivirus updated. If automatic
updates are available, configure your
antivirus to use them.
- Keep your permanent antivirus protection
enabled at all times.
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