Attackers using two recently-uncovered Java unpatched vulnerabilities, or "zero-days," have quickly expanded their reach by going mainstream, security experts said.
Mozilla, maker of Firefox, joined the chorus of advice that users should disable the current version of Oracle's Java. The company is also ready to automatically block the plug-in from running in its browser, although it has not yet pulled the trigger.
The exploit's breakout followed the addition of attack code to the notorious Blackhole exploit toolkit.
Multiple security firms, including FireEye and Websense, said late Tuesday (US time) that the Java exploit had been added to Blackhole, a popular hacker's tool that bundles numerous exploits and tries each in turn until it finds one that will work against a personal computer.
"Exploit code for the Java vulnerabilities has been added to the most prevalent exploit kit out there, Blackhole," said Websense in a short post on its company blog.
The addition of the exploit to Blackhole was cited by FireEye researcher Atif Mushtaq in a similar blog entry yesterday as the basis for a spike in attacks. "After seeing the reliability of this attack, I have no doubt in my mind that within hours the casualties will be in the thousands," said Mushtaq.
Today, Patrik Runald, director of security research at Websense, said his team had found more than 100 unique domains serving the Java exploit.
"The number is definitely growing...and because Blackhole has an updatable framework and already has a foothold on thousands of sites, we anticipate that the number of sites compromised with this new zero-day will escalate rapidly in the coming days," Runald said in an email reply to questions Wednesday.
Initially, the exploit was aimed at a small number of individuals or organisations.
It doesn't appear that the appearance of attack code in Metasploit, the open-source penetration testing framework used by both legitimate researchers and criminals, played a part in the quick dissemination of the exploit. According to Runald, the Blackhole exploit was based on earlier proof-of-concept code.
Yesterday, Michael Coates, Mozilla's director of security assurance, urged Firefox users to disable the browser's Java plug-in because Oracle has not issued fixes. Others, including US-CERT (United States Computer Emergency Readiness Team) have given the same advice, or recommended the more drastic measure of uninstalling Java entirely.
Firefox developers are also ready to issue a kill order for the vulnerable Java 7 plug-in, according to a discussion on its Bugzilla code change and bug-fixing database.
Mozilla has the ability to add extensions or plug-ins to the Firefox add-on blocklist if they cause significant security or performance issues. Firefox automatically queries the blocklist and notifies users before disabling the targeted add-ons.
"Oracle is unlikely to patch this ahead of their scheduled October update and that's plenty of time for evil-doers to profit if we don't block until then," said Daniel Veditz, a Firefox security engineer, on Bugzilla.
Oracle is scheduled to release its next Java security update Oct. 12.
Although the current exploits -- and Blackhole -- target only Windows PCs, some machines running OS X will also be vulnerable to attacks if hackers integrate the Java zero-days in Mac-specific malware.
Apple stopped bundling Java with OS X starting with 2011's Lion; this year's Mountain Lion also omits Java. Those users, however, may still have Java 7 installed. When a browser encounters a Java applet, OS X asks the user for permission to download the Oracle software.
People running the older Snow Leopard (2009) and Leopard (2007) are apparently not at risk, since Java 7 requires the more recent Lion and Mountain Lion. The unpatched vulnerabilities are present only in Java 7.
While more than half of all Macs were running Lion or Mountain Lion as of July 31, statistics on OS X Java 7 installations were unavailable.