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Copyright: Dr. Nikolai Bezroukov 1994-2013. Unpublished notes. Version 0.80.October, 2013
Contents : Foreword : Ch01 : Ch02 : Ch03 : Ch04 : Ch05 : Ch06 : Ch07 : Ch08 : Ch09 : Ch10 : Ch11 : Ch12 : Ch13
Chapter 7: Network worms
"The Zotob worm and several variations of it, known as Rbot.cbq, SDBot.bzh and Zotob.d, infected computers at companies such as ABC, CNN, The Associated Press, The New York Times, and Caterpillar Inc."
Zotob was discovered around August 12-13, 2005. August 13, 2005 was a Saturday and the epidemics happened two days later when users returned to their PCs from the weekend. Good chronology of events can be found at Zotob (computer worm) - Wikipedia, the free encyclopedia. See also Bozori.A-E (Zotob.E) Worm
The main target of the worm is Windows 2000. It represents minimal risk to XP and Windows 2003 as they require authentication that prevents a particular vulnerability from being exploited. Setting RestrictAnonymous=2 in the registry will disable non-authenticated sessions and prevent infection on Win2k systems.
Enabling port blocking on a built-in firewall is also a good preventive measure. As for many other network worms, disinfection in a sense of removal of worm is not enough: You need to apply Microsoft patch (Microsoft Security Bulletin MS05-039)
This worm, while not as bad as some previous (slammer/sapphire, code red, msblaster) is still a pain. It tries to spread to addresses with the same first 2 octets as the current machine (same class B networks). On 10 networks that limits it to the same network, unless you have VPN connections to other networks.
Initially it causes a huge initial spike in network traffic in corporate class
B networks but unlike some predecessors the spike was one time and short lived (less
then an hour). Some routers went down. Due to this some organizations overreacted
by shutting down their networks or PCs or both, inflicting more damage then the
worm itself. After the initial spike the worm just sits on infected
PCs essentially waiting for disinfection and there is no rush to do anything about
Only Windows 2000 PC are affected by the worm. Generally mass infection were typical only for large organizations with mass deployment of Windows 2000 desktops. The worm does not infect computers running Windows XP Service Pack 2 nor Windows 2003, as those systems are somewhat protected against the Windows Plug-and-Play vulnerability that the worm uses.
The code used in the Zotob worm to exploit the Microsoft PnP vulnerability addresses in MS05-039 relies on NULL sessions to exploit the target system. Default installations of Windows XP SP2 and Windows 2003 do not have NULL sessions enabled, and thus are not affected by the worm. See http://www.securityfocus.com/news/11281
On Windows 2000 the virus is effective only if:
This worm creates up to 300 threads to scan for vulnerable systems generating random class B address in the segment where the infected workstation is. For each generated address the worm is sending SYN packets to TCP Port 445 trying to exploit the vulnerability. Generation is a one time deal -- one for each infection.
When a vulnerable system is found, buffer overflow and shellcode is sent to the remote system, creating an FTP script (2pac.txt is the script file name) and launching FTP.EXE to download and execute the worm from the source system (ftp connection is established via TCP port 33333, haha.exe is fetched).
Worm propagation is a typical datacenter environment looks like a burst-style, one-time traffic explosion that can tale router down. After the worm is done with it, it generates almost no traffic. That's why most networks survived pretty well after the initial infection packets are all generated.
Summary of ports used:
Administrators can scan their segments using nmap -p 8888,33333 <segment> to detect infected computers. Please note that ports 445, 8888 and 33333 are blocked on many enterprise routers, so you can get results only within your local network segment. Please do not scan more then one C-class segment at a time.
Ports 8888 and 33333 should be blocked on all firewalls and routers untill the end of epidemics
Symantec has a primitive scanning (and that means very slow ;-) removal tool to clean the infections of W32.Zotob. Still that might be the easiest way to remove this worm for home users.
Microsoft also published manual recovery procedure:
To manually recover from infection by Worm:Win32/Zotob.A, follow these steps:
- Install security update MS05-039.
- Disconnect from the Internet.
- End the worm process.
- Delete the worm files from your computer.
- Delete the worm registry entries.
- Clean the system host file.
- Restart your computer.
- Take steps to prevent re-infection.
Install security update MS05-039To install MS05-039 using Windows Update
- Go to the Windows Update Web site at windowsupdate.microsoft.com.
- On the Windows Update site, click Scan for Updates. Windows Update scans your computer and returns a list of critical updates, including service packs.
- In the Pick updates to install list, click Critical Updates and Service Packs. Windows Update creates a list of the updates appropriate for your computer, including MS05-039 if it is not installed. Critical updates are selected for download automatically.
- Click Review and install updates, and then click Install Now. You may need to restart your computer after installing the updates.
Disconnect from the InternetTo help ensure that your computer is not actively infecting other computers, disconnect it from the Internet before proceeding. Print this Web page or save a copy on your computer; then unplug your network cable and disable your wireless connection. You can reconnect to the Internet after completing these steps.
End the worm processEnding the worm process will help stop your computer from infecting other computers as well as resolve the crashing, rebooting, and performance degradation issues caused by the worm.
To end the worm process
- Press CTRL+ALT+DEL once and click Task Manager.
- Click Processes and click Image Name to sort the running processes by name.
- Select the process botzor.exe, and click End Process.
Delete the worm files from your computerTo delete the worm files from your computer
If deleting the files fails, follow these steps to verify that botzor.exe is not running:
- Click Start, and click Run.
- In the Open field, type the name of the system folder, for example, C:\Winnt\system32\
- Click OK.
- Click Name to sort files by name.
- If botzor.exe is in the list, delete it.
- On the Desktop, right-click the Recycle Bin and click Empty Recycle Bin.
- Click Yes.
- Press CTRL+ALT+DEL once and click Task Manager.
- Click Processes and click Image Name to sort the running processes by name.
- Confirm that botzor.exe is not in the list.
Delete the worm registry entriesWorm:Win32/Zotob.A creates entries in the Windows registry that attempt to run the worm every time your computer restarts. These entries should be deleted.
To delete the worm registry entries
- On the Start menu, click Run.
- Type regedit and click OK.
- In the left pane, navigate to the key: HKLM\Software\Microsoft\Windows\CurrentVersion\Run
In the right pane, right-click the following value, if it exists:
- Click Delete and click Yes to delete the values.
- Repeate steps 3-4 for HKLM\Software\Microsoft\Windows\CurrentVersion\RunServices.
- Close Registry Editor.
Clean the system host fileThe worm makes changes to the system host file to prevent access to certain Web sites.
To clean the system host file.
- On the Start menu, click Run.
- Type notepad.exe and click OK.
- On the File menu, click Open…
- In the File name text box, type the name of the Windows directory folder and \system32\drivers\etc\hosts, for example, C:\winnt\system32\drivers\etc\hosts.
- Search for text that begins with "Botzor2005 Made By…"
- Select this text and all text that follows. Delete the selected text and save the file.
- Close Notepad.
Restart your computerTo restart your computer
- On the Start menu, click Shut Down.
- Select Restart from the drop-down list and click OK.
Take steps to prevent re-infectionDo not reconnect your computer to the Internet until the computer is protected from re-infection. See the "Preventing Infection" section for more information.
The worm copies the following file to the newly compromised computer and executes an FTP script contained within it:
Next it downloads executes the following copy of the worm from the previously created FTP server on the host computer:
The worm exists in at least two versions and you should also check for the file
botzor.exe in the WINDOWS SYSTEM directory and registry run keys are created to load the worm at startup:
Run "WINDOWS SYSTEM" = botzor.exe
RunServices "WINDOWS SYSTEM" = botzor.exe
An additional registry change is made:
SharedAccess "Start" = 4 (default is 3)
The HOSTS file is appended to block access to anti-virus websites:
Those changes can be easily checked manually even without any tools to detect the infection
Zotob (computer worm) - Wikipedia, the free encyclopedia
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ABUSE: IPs or network segments from which we detect a stream of probes might be blocked for no less then 90 days. Multiple types of probes increase this period.
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