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The Story of Conficker and the Industry Response

Terry Zink

On November 2, 2009, Microsoft released its seventh edition of the Security and Intelligence Report (SIR). The SIR provides an in-depth perspective on the changing threat landscape including software vulnerability disclosures and exploits, malicious software (malware), and potentially unwanted software. Using data derived from hundreds of millions of Windows computers, and some of the busiest online services on the Internet, this report also provides a detailed analysis of the threat landscape and the changing face of threats and countermeasures and includes updated data on privacy and breach notifications.

The following is an excerpt from the SIR, pp 29-32, about the Conficker worm and the industry response that showed an incredible amount of collaboration across vendors.

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Case Study: The Conficker Working Group

The appearance in late 2008 of Win32/Conficker, an aggressive and technically complex new family of worms, posed a serious challenge to security responders and others charged with ensuring the safety of the world's computer systems and data. ("Win32/Conficker Update," beginning on page 95, explains the technical details of the Conficker worm and the methods it uses to propagate.) Working together, however, the security community was able to react quickly to the threat and contain much of the damage, in the process establishing a potentially groundbreaking template for future cooperative response efforts. On October 23, 2008, Microsoft released critical security update MS08-067, addressing CVE-2008-4250, a vulnerability in the Windows Server service that could allow malicious code to spread silently between vulnerable computers across the Internet.

The vulnerability affected most currently supported versions of Windows, although architectural improvements in Windows Vista and Windows Server 2008 made them more difficult to exploit than earlier versions. Like the worms that plagued the Internet earlier this decade, malware that exploited the vulnerability would be able to spread without user interaction by taking advantage of the protocols computers use to communicate with each other across networks. For this reason, and because actual attack code that exploited the vulnerability was known to exist in the wild at the time, the MSRC took the unusual step of releasing MS08-067 "out of band" rather than wait for the next scheduled release of Microsoft security updates, which takes place on the second Tuesday of every month. Security Bulletin MS08-067 happened to be released on the last day of the eighth annual meeting of the International Botnet Task Force in Arlington, Virginia, a suburb of Washington, D.C., where attendees agreed to closely monitor developments around what appeared to be the first legitimately "wormable" vulnerability to be discovered in Windows in several years.

The November appearance of Win32/Conficker, the first significant worm that exploited the MS08-067 vulnerability, marked a major challenge for security researchers, due to the aggressive tactics several of its variants used to propagate. Despite this, researchers soon discovered a way to limit or eliminate the Conficker bot-herders' ability to issue instructions to infected computers. As described on page 96, the authors of the Conficker malware used an algorithm to generate 500 new domain names every day (250 for each of the first two Conficker variants discovered) to use for command-and-control servers. Computers infected with Conficker would attempt to contact each of these generated domain names every day. If the authors had a task they wanted the computers in the botnet to perform, they would simply use the same algorithm to generate domain names in advance and register a few of them, which they could then use to host command-and-control servers.

Fortunately, researchers from Microsoft and other organizations were able to reverse engineer the domain-name-generation algorithms used by the first two variants, designated Worm:Win32/Conficker.A and Worm:Win32/Conficker.B, soon after each variant was discovered. This enabled them to begin registering the domain names before the botnet operators could, thereby impeding the Conficker malware from obtaining new instructions. Initially, the researchers resorted to registering the domains commercially through the domain name registrars for the eight top-level domains (TLDs) (.com, .net, .org, .info, .biz, .ws, .cn, and .cc) used by Conficker, an approach that quickly became unworkable. Registering 500 domain names per day would cost thousands of (U.S.) dollars per day for the foreseeable future — and the cost would only increase if new variants appeared using different name-generation algorithms. It was clear that more help would be needed.

The Conficker Working Group Is Born

In January 2009, representatives from a number of security research companies and domain registrars, along with the anti-botnet Shadowserver Foundation, began discussing how best to implement a defensive Domain Name Service (DNS) strategy to handle domain registrations. To coordinate the significant amount of e-mail being generated by these discussions, the group established the CONFICKER e-mailing list on January 28, which drew a growing number of security researchers and members from law enforcement, academia, and industry, in addition to members representing each of the eight TLDs used by Conficker. Enlisting the support of the TLD operators would prove to be a vital step in containing the Conficker threat, enabling the group to block domain names more efficiently and at far less expense than would be possible through the commercial registration process.

By early February 2009, working group members had instituted a process for registering as many domain names as possible, before the Conficker operators could register them, and assigning them to IP addresses belonging to six sinkholes (server complexes designed to absorb and analyze malware traffic) operated by organizations belonging to the working group. Infected computers looking for command-and-control servers would contact the sinkholes instead, providing researchers with valuable telemetry for analyzing the spread of the worm. A number of Internet service providers (ISPs) were also able to use this telemetry data to identify infected computers.

Around the same time, the Internet Corporation for Assigned Names and Numbers (ICANN), which is responsible for allocating IP addresses and managing the Internet domain name system, invited the group to deliver a presentation on its domain registration efforts to a meeting of the ICANN board of directors. The board expressed its support for the program and assigned two staffers to help coordinate it. Despite these efforts, the Conficker operators were still able to register some domains before the working group could get to them. To mitigate this, researchers at Kaspersky Lab, an anti-malware vendor headquartered in Russia, worked with OpenDNS, a free network resolution service used by many organizations and individuals, to compute a year's worth of Conficker domain names and proactively point them at the group's sinkholes. Any infected computer belonging to an OpenDNS user would not be able to contact any of the Conficker command-and-control servers, even on domains the Conficker operators had been able to secure.

The formation of the Conficker Working Group (CWG) was officially announced to the public on February 12, 2009, as what a number of news stories characterized as an unprecedented example of global cooperation in the computer security industry, and a potential blueprint for dealing with threats in the future. The CWG had grown from an e-mail list for nine individuals to a group of more than 30 member organizations from around the world, coordinating complex activities through a robust communications infrastructure. On the day the CWG was announced, the group had successfully registered every Conficker domain name for the next 10 days, a genuine — if temporary — victory over the Conficker operators.

Setbacks and Triumphs

The domain registration task became exponentially more challenging on March 4, 2009, with the discovery of Worm:Win32/Conficker.D. Investigators reverse-engineered the new variant and determined that it was programmed to generate 50,000 new domain names a day across 110 TLDs, beginning on April 1, 2009. Though this seemed at first like an impossible hurdle to overcome, CWG members immediately began working to counter the effects of the upcoming change. As security researchers continued to analyze the Conficker.D malware, ICANN staffers began contacting the registries responsible for each of the affected TLDs seeking cooperation in registering or blocking the domains, and the CWG compiled "go packs" of information for Internet service providers and enterprises about the steps they should take to help keep their customers and employees safe.

April 1, 2009, came and went, with the world outside the security community noticing little or no change. By that time, however, ICANN had secured the cooperation of all 110 TLDs used by Conficker, and the global DNS community was active and prepared to deal with the Conficker threat. Rapid, effective collaboration across borders and organizational lines had proven instrumental in containing what has been, and remains, a significant threat to the world's computers and information.

The CWG Today

The CWG remains in place today, with more than 300 member organizations representing law enforcement, academia, and industry, and remains vigilant against new developments. In cooperation with ICANN and the DNS community, the CWG continues to block or register the 50,000 domain names generated each day by the Conficker algorithms. Each month the group supplies the 110 affected TLD operators with an updated list of generated domain names covering the next several months, so they can begin implementing countermeasures well in advance. Automated mechanisms verify that each domain name has been blocked before it is scheduled to be used and alert the CWG for any that have not, so activity for those domains can be closely monitored. Once in a while, a domain name generated by the algorithm happens to correspond to an existing domain owned by a legitimate party; in such cases, the CWG contacts the legitimate domain owner in advance and offers assistance managing the expected spike in traffic coming from infected computers.

In March, the group underwent a reorganization process to add structure and to segment its work by subject area to work more effectively. The group maintains a Web site at http://www.confickerworkinggroup.org with links to information in multiple languages about Conficker and resources that service providers and end users can use to determine if they are infected, and if so, what to do about it. The fight against Conficker is not over. The five identified variants continue to spread to new computers due to a lack of information or action on the part of some system administrators and end users. Even after Conficker recedes into insignificance, there will likely be other threats of similar magnitude to deal with in the future. As such threats appear, though, collaborative efforts, such as the CWG, can provide the global security community with unequaled tools for mitigation and resolution.

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The SIR contains other data on Conficker including how many machines were cleaned by the Microsoft Malicious Software Removal Tool and its comparison to other malware removed during the first half of 2009.

By Terry Zink, Program Manager
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Share your comments

I think Rick Wesson probably deserves a Gadi Evron  –  Nov 13, 2009 12:44 AM PST

I think Rick Wesson probably deserves a place of honour in your interesting text, though, as the guy who started it all and made it happen.

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