Cali.A

Summary

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The Cali worm was found on 10th of August 2004. It's a massmailer.

Removal

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Automatic action

Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.

More

Detailed instructions for F-Secure security products are available in the documentation found in the Downloads section of our Home - Global site.

You may also refer to the Knowledge Base on the F-Secure Community site for further assistance.

Technical Details

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Cali is packed with Yoda and UPX. It's packed size is 51270 bytes. Once unpacked it grows up to 100KiB.

The executable was compiled with Microsoft's Visual C++ compiler with the stack protection option enabled. It's possible to appreciate in the code this feature, which protects the stack by placing a 'canary' value between the function's local variables and the return address. In this scenario if a buffer overflow would occur, it would be detected before the function returns, making the exploitation of an overflow a non trivial task.

The stack protection is enabled with the /GS option. More documentation on its implementation can be found from "Compiler Security Checks In Depth":

https://go.microsoft.com/fwlink/?Linkid=7260

It's worth mentioning that some older worm could be taken over because of a buffer overflow in its networking code. It's interesting that malware writers are also paying attention to security related issues.

Once executed it creates a a mutex named:

"4D36E64A-W325-121E-BFC1-080C2BE11318"   

in order to avoid being run more than once. And copies itself to:

%WinDir%\system\services.exe   

A registry key will be set to point to the dropped file, the name of the key will be randomly chosen from:

BuildLab  RegDone  ccApps  Microsoft Visual SourceSafe  TEXTCONV  FriendlyTypeName  .Prog  WMAudio   

therefore, the registry key might look as follows:

[HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\]  "WMAudio" = "%WinDir%\system\services.exe"   

Where %WinDir% is the main Windows folder.

E-Mail spreading

When massmailing, it will attach itself with names such as:

office.exe  notes.exe  doom3demo.exe  resume.exe  files.exe  request.exe  info.exe  details.exe  result.exe  results.exe  install.exe  setup.exe  test.exe  google.exe  se_files.exe   

Detection

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Detection for Cali worm is available since the following FSAV updates:

Detection Type: PC
Database: 2004-08-10_01

Technical Details:Ero Carrera, August 10th, 2004