Security Experts:

Mac OS X Malware Builds Botnet More than 550,000 Strong

Security researchers say the Flashback malware hitting Mac OS X machines has built a powerful botnet of more than 550,000 computers.

According to researchers with Russian security firm Dr. Web, Flashback has been spreading recently on the back of a Java vulnerability patched by Oracle in February (CVE-2012-0507). The malware infects users redirected to a malicious site from either a compromise resource or traffic distribution system (TDS), the firm explained in an advisory. From there, JavaScript code is used to load the malicious Java-applet containing the exploit.

Mac Botnet“Attackers began to exploit CVE-2011-3544 and CVE-2008-5353 vulnerabilities to spread malware in February 2012, and after March 16 they switched to another exploit (CVE-2012-0507),” the firm noted. “The vulnerability has been closed by Apple only on April 3, 2012.”

Once on a system, the malware opens a backdoor and steals data. Using sinkhole technology, Dr. Web analysts redirected the botnet traffic to their own servers to count infected hosts. The 550,000 Macs identified only compromise a segment of the botnet, the firm stated, with most of the infected computers residing in the United States (56.6 percent).

Earlier this week, Apple issued a patch to stop the malware from compromising computers by shutting down security holes in Java 1.6.0_29. Mozilla took action as well, choosing to blacklist out-of-date versions of Java to protect users vulnerable to the attack.

“I would definitely commend them for adding outdated Java to their blacklist,” Coverity Senior Security Research Scientist Chris Valasek told SecurityWeek. “While this doesn’t solve all the security problems, it will make the user aware that an outdated, insecure version of Java is being used by Firefox.”

“Although blacklisting will work to a certain extent, it is not the perfect solution,” he added. “Getting the updates to the end-user and in the browser in seamless fashion is the most important. Remember, attacks against fully-patched version of Java do and will continue to happen. You can only protect from attacks that are known, not ones that are unknown.”

Intego, a security firm focused on Apple products, stated in a blog post that all of the servers they know to have been providing the Flashback malware seem to be offline. The command and control servers however remain active, meaning the Macs that are infected are still vulnerable to data theft and other activities, the firm said.

“This malware has changed greatly from its first incarnation,” according to the firm. “Initially a fake Adobe Flash installer (hence the name Flashback), it later changed to impersonate a Software Update dialog, before using Java vulnerabilities to install. It is likely that this malware will be back in another guise in the future. But for now, the most important thing users can do is make sure that they update Java – as well as apply any other security updates that they haven’t installed yet – to be protected in case the Flashback servers come back online.”

“Java has become a target for the same reason that web browsers in general have become targets,” Valasek said. “They are implemented in the most ubiquitous piece of software used by all peoples on all devices. The massive install base coupled with limited support for ASLR (address space layout randomization) and DEP (data execution prevention) make it the perfect target.”

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