Zotob.C is a new variant of Zotob. It spreads using a vulnerability in Windows Plug and Play service (MS05-039) and ASN.1 (MS04-007). This variant also has Mydoom e-mail spreading routine.
Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.
For general instructions on disinfecting a local network infection, please see Eliminating A Local Network Outbreak.
The worm is a packed PE executable file 31744 bytes long.
Installation to system
When run, the worm copies under %SYSTEM% directory using the name 'per.exe' and creates a named mutex 'B-O-T-Z-O-R' for making sure that only one copy of the worm is run at the same time.
Then it adds the following registry entries to ensure that it is started when a user logs on or the system is restarted:
- [HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices] "WINDOWS SYSTEM" = "per.exe"
The worm also adds the following registry key for diasabling shared access service:
- [HKLM\SYSTEM\CurrentControlSet\Services\SharedAccess] "Start" = "4"
The worm can spread by sending its infected attachment to e-mail addresses found on an infected computer. E-mail addresses are harvested from Windows address book and from files with the following extensions:
The worm avoids sending e-mails to e-mail addresses that contain any of the following substrings:
The e-mail message is composed from randomly chose subject line, body text and additional parts. The worm has a selection of attachment names that it uses for its attachment. The subject of infected e-mails are selected from the following variants:
Body of the text is selected from the following list:
- We found a photo of you in ...
- That's your photo!!?
- 0K here is it!
The attachment name is composed using predefined keywords. The keywords set is:
And extension keywords set are:
Spreading using exploits
The worm scans for systems vulnerable to Microsoft Windows Plug and Play service (MS05-039) and ASN.1 vulnerability (MS04-007) through TCP/445.
It creates 200 threads that connect to random IP addresses within the B-class (255.255.0.0) network of the infected system. First it tests connection to port 445 and if successful, it tries to exploit the PnP vulnerability. If the attack is successful, a shell (cmd.exe) is started and FTP script is transferred and executed on the remote machine. This script then downloads and executes the worm's file from the attacking machine. Please see the details of this attack from Zotob.A description:
If the PnP attack fails, the worm tries to exploit ASN.1 vulnerability (MS04-007). The attack is very similair to PnP attack - an FTP script is executed on a remote host and the built-in FTP server is then used to transfer the worm's file to exploited system. ASN.1 exploit is reported to work on (unpatched) Windows 2000 SP 2-4 and Windows XP SP 0-1.
Please see the following pages for detailed information on the vulnerabilities:
The worm tries to connect to IRC channel at predefined address. The attacker who knows channel password can instruct the bot to execute the following actions:
- Disconnect/reconnect from the IRC channel
- Request system information
- Download and execute files
- Remove worm from the system
- Manipulate system security settings
Zotob.C modifies system hosts file in order to disable access to certain sites. Following hostnames are redirected to localhost IP address (127.0.0.1):
The worm also writes the following text to hosts file:
- Botzor2 pnp+asn+mail spread. Greetz to good friend Coder. Based On HellBot3 f-secure,sophos ok wait bitchs!!!