Worm:W32/NetSky.S

The worm's file is a PE executable 18432 bytes long packed with PE-Patch and UPX file compressors. Some of the worm's text strings are encrypted.

Installation to system

Upon execution NetSky.S copies itself as EastAV.exe file to Windows folder and adds a startup key for this file into System Registry:

[HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run] "EasyAV" = "%WinDir%\EasyAV.exe"

where %WinDir% represents Windows folder name.

Additionally the worm drops the uinmzertinmds.opm file in Windows folder. This file contains the MIME-encoded copy of the worm's executable that will be sent in emails.

The worm always has 2 of its processes in Windows memory. If one process gets killed, the remaining one restarts it. The worm also protects its file and startup key in the Registry from being deleted. All the above makes manual disinfection a challenging task.

Spreading in email

Before spreading in email the worm collects email addresses. It scans all files on all drives from C: to Z: except CD-ROM drives. If any file with the following extensions is found, the worm opens it and searches for email addresses there:

.eml .txt .php .cfg .mbx .mdx .asp .wab .doc .vbs .rtf .uin .shtm .cgi .dhtm .adb .tbb .dbx .pl .htm .html .sht .oft .msg .ods .stm .xls .jsp .wsh .xml .mht .mmf .nch .ppt

The worm spreads itself in emails It sends messages with different subject lines, body text and attachment names. Here's the list of subjects that the worm uses:

Hi Hello Re: Hi Re: Hello Approved Re: Approved Thank you! Re: Thanks you! Request Re: Request Your document Re: Your document Your details Re: Your details Your information Re: Your information My details Re: My details Important Re: Important

The message body is composed from 4 different string arrays:

Array1:

Hi! Hello! Hello!

Array2:

Please read the . Please have a look at the . Here is the . The is attached. Please see the . I have sent the . The requested is attached! Here is the document. See the document for details. Please have a look at the attached document. Please read the attached document. Your file is attached to this mail. Please, . Your is attached. My is attached. I have found the . Approved, here is the document. For more information see the attached document. For more details see the attached document. Please read quickly. Please notice the attached document. Please notice the attached . Your . I have spent much time for your document. I have spent much time for the . The . My . Note that I have attached your document.

Array3:

Please read the . Please have a look at the . Here is the . The is attached. Please see the . I have sent the . The requested is attached! Here is the document. See the document for details. Please have a look at the attached document. Please read the attached document. Your file is attached to this mail. Please, . Your is attached. My is attached. I have found the . Approved, here is the document. For more information see the attached document. For more details see the attached document. Please read quickly. Please notice the attached document. Please notice the attached . Your . I have spent much time for your document. I have spent much time for the . The . My . Note that I have attached your document.

Array4:

Please read the . Please have a look at the . Here is the . The is attached. Please see the . I have sent the . The requested is attached! Here is the document. See the document for details. Please have a look at the attached document. Please read the attached document. Your file is attached to this mail. Please, . Your is attached. My is attached. I have found the . Approved, here is the document. For more information see the attached document. For more details see the attached document. Please read quickly. Please notice the attached document. Please notice the attached . Your . I have spent much time for your document. I have spent much time for the . The . My . Note that I have attached your document.

The attachment name is selected and the <string> value for the message body is selected from the following variants:

Please read the . Please have a look at the . Here is the . The is attached. Please see the . I have sent the . The requested is attached! Here is the document. See the document for details. Please have a look at the attached document. Please read the attached document. Your file is attached to this mail. Please, . Your is attached. My is attached. I have found the . Approved, here is the document. For more information see the attached document. For more details see the attached document. Please read quickly. Please notice the attached document. Please notice the attached . Your . I have spent much time for your document. I have spent much time for the . The . My . Note that I have attached your document.

The infected attachment has .PIF extension and can also contain random numbers in its name. The worm does not spread itself from 13th to 17th of April 2004.

Backdoor

The worm has a backdoor that listens on TCP port 6789. It allows to download and execute files on an infected computer.

Payload

Netsky.S has a payload. It performs a DoS (Denial of Service) attack on the following websites from 14th to 23rd of April 2004:

Please read the . Please have a look at the . Here is the . The is attached. Please see the . I have sent the . The requested is attached! Here is the document. See the document for details. Please have a look at the attached document. Please read the attached document. Your file is attached to this mail. Please, . Your is attached. My is attached. I have found the . Approved, here is the document. For more information see the attached document. For more details see the attached document. Please read quickly. Please notice the attached document. Please notice the attached . Your . I have spent much time for your document. I have spent much time for the . The . My . Note that I have attached your document.

Additional Info

This worm variant also contains a message from the author of the worm. Bagle is not mentioned there and taking into account that Netsky doesn't uninstall Bagle any longer, we consider the war to be over (at least for now).