Zero Day Java Vulnerability Allows McRat Trojan Infections

A newly discovered zero-day vulnerability in the most recent versions of Java 6 and Java 7 is being actively exploited by attackers to install malicious software on vulnerable PCs.

"We detected a brand new Java zero-day vulnerability that was used to attack multiple customers," FireEye security researchers Darien Kindlund and Yichong Lin said in a blog posted Thursday. "Specifically, we observed successful exploitation against browsers that have Java v1.6 update 41 and Java v1.7 update 15 installed," they said, referring to the two most recently released versions of Java 6 and Java 7.

The discovery of the new bug (CVE-2013-1493) makes for the third Java zero-day vulnerability to have been reported to Oracle this week.

So far, the FireEye researchers have publicly detailed the new vulnerability only in broad terms: "Not like other popular Java vulnerabilities in which [the] security manager can be disabled easily, this vulnerability leads to [an] arbitrary memory read and write in [the] JVM [Java virtual machine] process," they said.

[ Does your business depend on Java? Here's how to stay secure. 10 Facts: Secure Java For Business Use. ]

In the attack they spotted, a malicious JAR (Java archive) file is used to exploit the vulnerability and then target memory used by the Java security manager. If the exploit finds that the security manager is active, it attempts to overwrite the memory used by the security manager, thus disabling the functionality.

"Upon successful exploitation, it will download a McRAT executable ... from same server hosting the JAR file and then execute it," said Kindlund and Lin. McRAT is a remote access Trojan (RAT) designed to download further malware onto an infected PC.

Independent security researcher Eric Romang noted Friday in a blog post that the new "yet another Oracle Java 0day" was only being detected by 21 out of 46 antivirus scanners tested via VirusTotal, leading him to suggest that the exploit might already be built into an automated crimeware toolkit.

Oracle last released an emergency update for Java just 10 days ago, including what was billed as the final-ever public release of an update for Java 6, which has now been officially retired. That emergency update fixed a vulnerability that was being exploited by attackers to bypass the Java sandbox. It followed another emergency update from Oracle, released at the beginning of February, that patched 50 bugs in Java.

News of the new vulnerability brought fresh calls from security experts to disable the Java browser plug-in -- note that JavaScript is not at risk -- if at all possible. "Take care or uninstall Java (or both)," according to a tweet from French security firm Vupen Security.

The FireEye researchers offered similar advice: "We urge users to disable Java in your browser until a patch has been released; alternatively, set your Java security settings to "High" and do not execute any unknown Java applets outside of your organization," they said.

Meanwhile, veteran Java bug hunter Adam Gowdiak, CEO and founder of Poland-based Security Explorations, Thursday sent an email update to the Bugtraq mailing list, reporting on the status of the two Java vulnerabilities he discovered this week -- mentioned above -- which he's detailed to Oracle, including proof-of-concept exploit code.

Of the two bugs, Oracle confirmed what Gowdiak labeled "issue 55." No details of the vulnerabilities have been publicly released, except that they involve a Java reflection vulnerability. But according to Gowdiak's email, Oracle dismissed "issue 54," saying that merely provides "allowed behavior" in Java.

Gowdiak, however, disagreed with Oracle's assessment, saying that a similar, previously discovered problem "leads to access denied condition and a security exception," which he considers to be a security flaw. "If Oracle sticks to their assessment we'll have no choice than to publish details of issue 54," he said.

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