W32.Blaster.Worm
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| Discovered on: August 11, 2003 |
| Last Updated on: August 11, 2003 04:38:47 PM |
W32.Blaster.Worm is a worm that will exploit the DCOM RPC vulnerability (described in Microsoft Security Bulletin MS03-026) using TCP port 135. It will attempt to download and run the file Msblast.exe.
You should block access to TCP port 4444 at the firewall level, and block the following ports, if they do not use the applicaitons listed:
- TCP Port 135, "DCOM RPC"
- UDP Port 69, "TFTP"
The worm also attempts to perform a Denial of Service on windowsupdate.com. This is an attempt to disable your ability to patch you computer against the DCOM RPC vulnerability.
Click here for more information on the vulnerability being exploited by this worm and to find out which Symantec products can help mitigate risk from this vulnerability.
NOTE: This threat will be detected by virus definitions having:
Defs Version: 50811s
Sequence Number: 24254
Extended Version: 8/11/2003 rev. 19
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August 11, 2003 |
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August 11, 2003 |
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Intelligent Updater definitions are released daily, but require manual download and installation.
Click here to download manually. |
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LiveUpdate virus definitions are usually released every Wednesday.
Click here for instructions on using LiveUpdate. |
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Damage
Distribution
When W32.Blaster.Worm is executed, it does the following:
- Creates a Mutex named "BILLY". If the mutex exists, the worm will exit.
- Adds the value:
"windows auto update"="msblast.exe"
to the registry key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
so that the worm runs when you start Windows.
- Calculates the IP address, based on the following algorithm, 40% of the time:
Host IP: A.B.C.D
sets D equal to 0.
if C > 20, will subtract a random value less than 20.
Once calculated it will start attempting to exploit the computer based on A.B.C.0 and count up.
NOTE: This means the Local Subnet will become saturated with port 135 requests prior to exiting the local subnet.
- Calculates the IP address, based on many random numbers, 60% of the time:
A.B.C.D
set D equal to 0.
sets A, B, and C to random values between 0 and 255.
- Sends data on TCP port 135 that may exploit the DCOM RPC vulnerabilty to allow the following actions to occur on the vulnerable computer:
Create a hidden Cmd.exe remote shell that will listen on TCP port 4444.
NOTE: Due to the randomness with how it constructs the exploit data, it may cause computers to crash if it sends incorrect data.
- Listens on UDP port 69. When it recieves a request, it will send back the Msblast.exe binary.
- Sends the commands to the remote computer to connect back to the infected host and download and run the Msblast.exe.
- If the current month is after August, or if the current date is after the 15th it will perform a denial of service on "windowsupdate.com"
With the current logic, the worm will activate the Denial of Service attack on the 16th of this month, and continue until the end of the year.
The worm contains the following text which is never displayed:
I just want to say LOVE YOU SAN!!
billy gates why do you make this possible ? Stop making money and fix your software!!
Symantec ManHunt
Symantec ManHunt Protocol Anomaly Detection technology detects activity associated with this exploit as "Portscan". Although ManHunt can detect activity associated with this exploit with the Protocol Anomaly Detection technology, the "Microsoft DCOM RPC Buffer Overflow" custom signature, released in Security Update can be used for exactly identifying the exploit being sent.
Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":
- Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
- If a blended threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
- Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
- Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
- Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
- Isolate infected computers quickly to prevent further compromising your organization. Perform a forensic analysis and restore the computers using trusted media.
- Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.
Important Note: W32.Blaster.Worm exploits the DCOM RPC vulnerability. This is described in Microsoft Security Bulletin MS03-026, and a patch is available from that location. You must download and install the patch. In many cases, you will have to do this before you can continue with the removal instructions. If you are not able to remove the infection or prevent reinfection using the instructions that follow, first download and install the patch.
- Disable System Restore (Windows Me/XP).
- Update the virus definitions.
- Do one of the following:
- Windows 95/98/Me: Restart the computer in Safe mode.
- Windows NT/2000/XP: End the Trojan process.
- Run a full system scan and delete all the files detected as W32.Blaster.Worm.
- Reverse the changes that the Trojan made to the registry.
For details on each of these steps, read the following instructions.
1. Disabling System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.
Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.
Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.
For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:
For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article, "Antivirus Tools Cannot Clean Infected Files in the _Restore Folder," Article ID: Q263455. 2. Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:
- Running LiveUpdate, which is the easiest way to obtain virus definitions: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).
- Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater).
The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.
3. Restarting the computer in Safe mode or ending the Worm processWindows 95/98/Me
Restart the computer in Safe mode. All the Windows 32-bit operating systems, except for Windows NT, can be restarted in Safe mode. For instructions on how to do this, read the document, "How to start the computer in Safe Mode."
Windows NT/2000/XP
To end the Trojan 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 msblast.exe.
- If you find the file, click it, and then click End Process.
- Exit the Task Manager.
4. Scanning for and deleting the infected files
- Start your Symantec antivirus program 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 W32.Blaster.Worm, click Delete.
5. Reversing the changes made to the registry
CAUTION: Symantec strongly recommends that you back up the registry before making any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified keys only. Read the document, "How to make a backup of the Windows registry," for instructions.
- 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:
"windows auto update"="msblast.exe"
- Exit the Registry Editor.
Write-up by: Douglas Knowles
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