Discovered: November 29, 2002
Updated: December 03, 2002 3:19:23 PM
Infection Length: 173,056 bytes
Systems Affected: Windows
Backdoor.Coreflood is a Trojan horse that opens a back door on the compromised computer.
Antivirus Protection Dates
- Initial Rapid Release version November 29, 2002
- Latest Rapid Release version July 20, 2019 revision 016
- Initial Daily Certified version November 29, 2002
- Latest Daily Certified version July 21, 2019 revision 002
- Initial Weekly Certified release date December 04, 2002
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.
This Trojan may be downloaded and installed by another threat, which may have been downloaded while visiting compromised websites.
When executed, the Trojan copies itself as the following file:
%System%\[RANDOM CHARACTERS FILE NAME ONE].ocx
It then creates the following files:
- %System%\[RANDOM CHARACTERS FILE NAME TWO].dat
- %System%\[RANDOM CHARACTERS FILE NAME THREE].dat
- %System%\[RANDOM CHARACTERS FILE NAME FOUR].dat
- %System%\[RANDOM CHARACTERS FILE NAME FIVE].dat
- %System%\[RANDOM CHARACTERS FILE NAME SIX].dat
Next, the Trojan creates the following registry entry to alter Explorer settings:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\ShellIconOverlayIdentifiers\usrcoind\"(Default)" = "[RANDOM CLSID]"
It then modifies the following registry entry to alter Explorer settings:
The Trojan then creates the following registry entries to register itself as a COM object:
- HKEY_CLASSES_ROOT\CLSID\[RANDOM CLSID]\"(Default)" = "usrcoind"
- HKEY_CLASSES_ROOT\CLSID\[RANDOM CLSID]\InprocServer32\"(Default)" =
- "%System%\[RANDOM CHARACTERS FILE NAME ONE].ocx"
- HKEY_CLASSES_ROOT\CLSID\[RANDOM CLSID]\InprocServer32\"ThreadingModel" = "Apartment"
It may then inject itself into the following processes:
Next, the Trojan monitors Internet traffic in order to steal credentials associated with online payment systems.
It can also monitor traffic when visiting URLs containing the following strings:
The Trojan then opens a back door, allowing an attacker to perform the following commands on the compromised computer:
The Trojan may perform any of the following actions:
- Download and run other malicious threats
- End processes
- Log a user off the computer
- Opens a command shell and waits for the commands from the remote host
- Restart itself
- Shut down the computer
- Steal information and then it to a remote host
The Trojan also uses code from the following file, which is a jailbreak utility tool:
It then exports certificates that have been marked as non-exportable from the Windows certificate store. These forged certificates could then be used for unauthorized access to banking sites, for example.
Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":
- Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
- 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.
- Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
- Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
- Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
- Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
- If a 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.
- Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
- Isolate compromised computers quickly to prevent threats from spreading further. 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.
- If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
- For further information on the terms used in this document, please refer to the Security Response glossary.
You may have arrived at this page either because you have been alerted by your Symantec product about this risk, or you are concerned that your computer has been affected by this risk.
Before proceeding further we recommend that you run a full system scan . If that does not resolve the problem you can try one of the options available below.
FOR BUSINESS CUSTOMERS
If you are a Symantec business product user, we recommend you try the following resources to remove this risk.
Identifying and submitting suspect files
Submitting suspicious files to Symantec allows us to ensure that our protection capabilities keep up with the ever-changing threat landscape. Submitted files are analyzed by Symantec Security Response and, where necessary, updated definitions are immediately distributed through LiveUpdate™ to all Symantec end points. This ensures that other computers nearby are protected from attack. The following resources may help in identifying suspicious files for submission to Symantec.
- Run Symantec Power Eraser in Symantec Help (SymHelp)
- About Symantec Power Eraser
- Symantec Power Eraser User Guide
How to reduce the risk of infection
The following resource provides further information and best practices to help reduce the risk of infection.
Protecting your business network
FOR NORTON CUSTOMERS
If you are a Norton product user, we recommend you try the following resources to remove this risk.
How to reduce the risk of infection
The following resources provide further information and best practices to help reduce the risk of infection.
- Operating system updates to fix vulnerabilities
- File sharing protection
- Disable Autorun (CD/USB)
- Best practices for instant messaging
- Best practices for browsing the Web
- Best practices for email
The following instructions pertain to all current Symantec antivirus products.
1. Performing a full system scan
How to run a full system scan using your Symantec product
2. Restoring settings in the registry
Many risks make modifications to the registry, which could impact the functionality or performance of the compromised computer. While many of these modifications can be restored through various Windows components, it may be necessary to edit the registry. See in the Technical Details of this writeup for information about which registry keys were created or modified. Delete registry subkeys and entries created by the risk and return all modified registry entries to their previous values.
Writeup By: Jeet Morparia