McAfee Labs

Malware in Recent Korean DDoS Attacks Destroys Systems

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By on Mar 07, 2011

There has been quite a bit of news recently about distributed denial of services (DDoS) attacks against a number of South Korean websites. About 40 sites– including the Presidential, National Intelligence Service, Foreign Ministry, Defense Ministry, and the National Assembly–were targeted over the weekend, beginning around March 4 at 10 a.m. Korean time. These assaults are similar to those launched in 2009 against sites in South Korea and the United States and although there is no direct evidence connecting them so far, they do bear some similarities.

DDoS attacks have occurred with more and more frequency, but one of the things that makes this attack stand out is its use of destructive payloads. Our analysis of the code used in the attack shows that when a specific timezone is noted by the malware it destroys the infected computer’s master boot record. If you want to destroy all the data on a computer and potentially render it unusable, that is how you would do it.

The malware in the Korean attacks employs an unusual command and control (C&C) structure. Instead of receiving commands directly from its C&C servers, the malware contacts two layers of servers. The first layer of C&C servers is encoded in a configuration file that can be updated at will by the botnet owner. These C&C servers simply provide a list of servers in the second layer, which will provide additional instructions. Looking at the disbursement of the first-layer C&Cs gives us valuable insight into the malware’s global footprint. Disbursement across this many countries increases resilience to takedowns. (Click on chart for details.)

This is further supported because the list of first-layer servers can be updated at any time.

The red code blocks deal with contacting the first-layer C&C server, the green code blocks retrieve the list of the second-layer servers, and the blue code blocks handle file downloads from the second-layer servers.

Botnets of infected computers usually receive commands directly and carry out the nefarious intent of their controllers. In this case, however, the C&C application behaves more like a downloader. Instead of directly interpreting commands, the application simply downloads files to the local hard disk. Secondary malware components that run independently of the main service find these files and then evaluate their contents to carry out an attack.

The two layers make it harder to analyze the malware because an analyst must understand many components and cannot simply follow the code flow within one malware binary. However, forensics are easier because in postmortem we can identify which task files have been created on an infected computer.

The malware in its current incarnation was deployed with two major payloads:

  • DDoS against chosen servers
  • Self-destruction of the infected computer

Although the DDoS payload has already been reported elsewhere, the self-destruction we discussed earlier in this post is the more pressing issue.

When being installed on a new computer, the malware records the current time stamp in the file noise03.dat, which contains the amount of days this computer is given to live. When this time is exceeded, the malware will:

  • Overwrite the first sectors of all physical drives with zeroes
  • Enumerate all files on hard disk drives and then overwrite files with specific extensions with zeroes

The service checks for task files that can increase the time this computer is allowed to live, so the botmaster can keep the botnet alive as long as needed. However, the number of days is limited to 10. Thus any infected computer will be rendered unbootable and data will be destroyed at most 10 days after infection! To protect against tampering, the malware will also destroy all data when the system time is set before the infection date.

The list of file extensions that will be overwritten is particularly interesting. It contains typical document data:

  • doc, docx, docm
  • xls, xlsx
  • pdf, eml (Outlook Email)

The list also contains some programming-language file extensions, such as c, cpp, h, and java. Wonder what they thought would be on the infected machines? Or did they already know?

One thing is clear: This is a serious piece of malware. It uses resilience techniques to avoid a takedown and even has destructive capabilities in its payload. This year is quickly shaping up to be a period of serious attacks and escalations on the cyberfrontier.

UPDATE

Our standalone malware-removal tool Stinger has been updated with a more generic detection of the malware involved in this attack. Stinger is available for download here.

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