WORM_SKYSTLR.A

 Analysis by: Francis Xavier Antazo

 ALIASES:

Virus:Win32/Sality.gen!enc (Microsoft); Virus.Win32.Sality.q, (Kaspersky); W32.Sality.U (Symantec);

 PLATFORM:

Windows

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:
 INFORMATION EXPOSURE:

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet, Dropped by other malware

This worm arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

It modifies the affected system's HOSTS files. This prevents users from accessing certain websites.

  TECHNICAL DETAILS

File Size:

708096 bytes

File Type:

EXE

Memory Resident:

Yes

Payload:

Modifies HOSTS file, Terminates processes, Steals information

Arrival Details

This worm arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

Autostart Technique

This worm adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows \CurrentVersion\Run
SystemDLL.MICROSOFT = “{malware path}\{malware filename}”

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows \CurrentVersion\Run
SystemDLL.MICROSOFT = “{malware path}\{malware filename}”

Other System Modifications

This worm adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows \CurrentVersion\Policies\
System"
DisableTaskMgr = "1"

HKEY_CURRENT_USER\Software\Microsoft\
Windows \CurrentVersion\Explorer\
Advanced
Hidden = "0"

Propagation

This worm drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

The said .INF file contains the following strings:

[autorun]
open={Drive Letter}:\HDDFile.com
shellexecute={Drive Letter}:\

It uses any of the following Simple Mail Transfer Protocol (SMTP) servers:

  • smtp.gmail.com

Process Termination

This worm terminates the following processes if found running in the affected system's memory:

  • anubis
  • ashWebSv
  • avgemc
  • bdagent
  • cpf
  • avp
  • keyscrambler
  • mbam
  • egui
  • npfmsg
  • ollydbg
  • outpost
  • vpcmapvmsrvc
  • wireshark

HOSTS File Modification

This worm modifies the affected system's HOSTS files to prevent a user from accessing the following websites:

  • www.virustotal.com
  • www.bitdefender.com
  • www.virusscan.jotti.org
  • www.scanner.novirusthanks.org
  • www.chip.de
  • www.vscan.novirusthanks.org
  • www.avira.de
  • www.avast.com

Stolen Information

The stolen information is saved in the following file:

  • %User Temp%\firefox.txt
  • %User Temp%\data.txt
  • %User Temp%\mess.txt
  • %User Temp%\astlog.txt
  • %User Temp%\mailpv.txt
  • %User Temp%\RouterPassView.txt
  • %User Temp%\iepv.txt
  • %User Temp%\OperPassView.txt
  • %User Temp%\ChromePass.txt

(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

NOTES:

This worm is infected with PE_SALITY.

It drops the following copy of itself on other drives aside from %SystemRoot%:

  • {Drive Letter}:\HDDFile.com

It retrieves the following information from the system:

  • passwords covered by asterisks on open windows
  • Chrome usernames and passwords
  • Dial-up usernames and passwords
  • Firefox usernames and passwords
  • IE usernames and passwords
  • Opera usernames and passwords
  • router usernames and passwords
  • account details from the following email clients:

    Outlook Express
    Microsoft Outlook 2000
    Microsoft Outlook 2002/2003/2007/2010
    Windows Mail
    Windows Live Mail
    IncrediMail
    Eudora
    Netscape 6.x/7.x
    Mozilla Thunderbird
    Group Mail Free
    Yahoo! Messenger application
    MSN/Windows/Live Messenger application
    Gmail Notifier application
    Google Desktop
    Google Talk
  • passwords from the following instant messaging applications:

    MSN Messenger
    Windows Messenger
    Windows Live Messenger
    Yahoo Messenger
    Google Talk
    ICQ Lite 4.x/5.x/2003
    AOL Instant Messenger
    AIM 6.x
    AIM Pro
    Trillian
    Trillian Astra
    Miranda
    GAIM/Pidgin
    MySpace IM
    PaltalkScene
    Digsby

  SOLUTION

Minimum Scan Engine:

9.750

FIRST VSAPI PATTERN FILE:

11.938.04

FIRST VSAPI PATTERN DATE:

24 Sep 2015

VSAPI OPR PATTERN File:

11.939.00

VSAPI OPR PATTERN Date:

25 Sep 2015

Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.

Step 2

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

Delete this registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • SystemDLL.MICROSOFT = “{malware path}\{malware filename}”
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • SystemDLL.MICROSOFT = “{malware path}\{malware filename}”
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System"
    • DisableTaskMgr = "1"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • Hidden = "0"

Step 5

Search and delete AUTORUN.INF files created by WORM_SKYSTLR.A that contain these strings

[ Learn More ]
  • [autorun]
  • open={Drive Letter}:\HDDFile.com
  • shellexecute={Drive Letter}:\

Step 6

Search and delete this file

[ Learn More ]
There may be some files that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the "More advanced options" option to include all hidden files and folders in the search result.
  • %User Temp%\firefox.txt
  • %User Temp%\data.txt
  • %User Temp%\mess.txt
  • %User Temp%\astlog.txt
  • %User Temp%\mailpv.txt
  • %User Temp%\RouterPassView.txt
  • %User Temp%\iepv.txt
  • %User Temp%\OperPassView.txt
  • %User Temp%\ChromePass.txt

Step 7

Remove these strings added by the malware/grayware/spyware in the HOSTS file

[ Learn More ]
    • 127.0.0.1 www.virustotal.com
    • 127.0.0.1 www.bitdefender.com
    • 127.0.0.1 www.virusscan.jotti.org
    • 127.0.0.1 www.scanner.novirusthanks.org
    • 127.0.0.1 www.chip.de
    • 127.0.0.1 www.vscan.novirusthanks.org
    • 127.0.0.1 www.avira.de
    • 127.0.0.1 www.avast.com

Step 8

Restart in normal mode and scan your computer with your Trend Micro product for files detected as WORM_SKYSTLR.A. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.


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