Yahoo Hit by Java Malware Outbreak: Lessons Learned From the Attack

NEWS ANALYSIS: The Yahoo malware advertising hack proves that hackers don't necessarily need to employ some form of new, exotic attack to exploit users.

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When you don't control all content that flows onto a site, there is always the potential risk that malicious malware could be sneaking in. That's what happened to Internet giant Yahoo over the weekend as malicious ads were able to infect unsuspecting users. Frankly, I'm not surprised.

Ad platforms have been the subject of much security research and attacks over the years. The basic technology that most ad platforms (including Yahoo) use to insert themselves onto Web pages is the HTML iFrame tag. The iFrame enables embedded content and code on a given page, and I have always considered its use a security risk.

In the Yahoo exploit, security firm Fox-IT reported that the malicious ads were combined with common exploit kits. Yahoo could have—and likely should have—known better as advertising-based attacks are nothing new.

Even this very site has been the victim of advertising malware attacks. Back in 2009, eWEEK and other Ziff Davis Enterprise sites were affected by a malware advertising attack. In that 2009 incident, the malware was exploiting flaws in Adobe Reader and Acrobat.

In the new Yahoo malware advertising attack, vulnerabilities in Oracle's Java are to blame. In a statement sent to media, Yahoo noted that it has now fixed the issue which affected some of its European sites over a four-day period from Dec. 31 to Jan. 3.

The potential for malware ads infecting users is nontrivial and can have a wide-reaching impact. In a Black Hat USA 2013 session, security researchers from White Hat security explained how malware ads could potentially enable a million browsers to become part of a hacker botnet.

In the White Hat presentation, the security researchers found that the ad networks simply just were not checking JavaScript that was embedded in the advertising code.

From an advertising network perspective, it's not always easy to analyze every ad, but I think that it is absolutely fundamental that ad networks take responsibility and ensure the ads they serve are malware-free. Yes, I know that in the modern era of interactive ads, where JavaScript is the norm, and much of that JavaScript can run on a third-party servers, ad platforms don't directly see the code—but that doesn't matter. Ad networks should take steps to get code and approve it to ensure it is malware-free.

The other issue here, though, is about Java. The Yahoo malware exploited old Java vulnerabilities, and if users were all up-to-date, then simply put, they couldn't be exploited.

Updating Java is something that all Web users should be doing as a means to prevent exploitation. Going a step further, given the volume of Java exploits, both known and unknown, that exist in the wild today, users might consider disabling Java altogether if it's not needed.

The Yahoo malware advertising hack proves that, once again, hackers don't necessarily need to employ some form of new, exotic attack to exploit users. Attacking users via embedded iFrames and delivering malware that attacks vulnerabilities that should already have been patched can still be effective in 2014.

Sean Michael Kerner is a senior editor at eWEEK and Follow him on Twitter @TechJournalist.

Sean Michael Kerner

Sean Michael Kerner

Sean Michael Kerner is an Internet consultant, strategist, and contributor to several leading IT business web sites.