Symantec Security Response
symantec.com
Backdoor.Berbew.B
Risk Level 1: Very Low
Discovered: April 8, 2004
Updated: April 16, 2004 05:26:19 PM PDT
Type: Trojan Horse
Systems Affected: Windows 2000, Windows 95, Windows 98, Windows Me, Windows NT, Windows Server 2003, Windows XP
SUMMARY
Backdoor.Berbew.B is a Backdoor Trojan horse that allows a compromised computer to be used as a Web proxy. This Trojan also attempts to steal cached passwords from an infected computer.
Protection
* Virus Definitions (LiveUpdate™ Weekly) April 12, 2004
* Virus Definitions (Intelligent Updater) April 8, 2004
Threat Assessment
Wild
* Wild Level: Low
* Number of Infections: 0 - 49
* Number of Sites: 0 - 2
* Geographical Distribution: Low
* Threat Containment: Easy
* Removal: Easy
Damage
* Damage Level: Low
Distribution
* Distribution Level: Low
TECHNICAL DETAILS
When Backdoor.Berbew.B is executed, it performs the following actions:
1. Copies itself as %System%\<8 random characters>.exe.
Note: %System% is a variable. The Trojan locates the System folder and copies itself to that location. By default, this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).
2. Creates a file, %System%\<8 random characters>.dll, which launches <8 random characters>.exe in the process space of explorer.exe. This hides the Trojan from process viewers, such as the Windows Task Manager.
3. Adds the values:
* "(Default)" = "%System%/<8 random characters>.dll"
* "ThreadingModel" = "Apartment"
to the registry key:
HKEY_CLASSES_ROOT\CLSID\{79FB9088-19CE-715E-D900-216290C5B738}\InProcServer32
which loads the .dll file every time Windows starts.
4. Adds the value:
"Web Event Logger" = "{79FB9088-19CE-715E-D900-216290C5B738}"
to the registry key:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\ShellServiceObjectDelayLoad
5. Listens on two configurable TCP ports that act as proxy servers. By default, this is TCP ports 9999 and 7777.
6. Listens on TCP ports 32121 and 23232 and waits for commands from the attacker.
7. Collects confidential information, such as passwords, from cached data entered into Internet Explorer forms. Then, the Trojan sends this information to predetermined URLs.
Recommendations
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 (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
* 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, .pi |
