Internet registrar is notorious for two things: domain names and risque super bowl commercials. The infamy began in 2005, when GoDaddy paid $4.8 Million for two 30 second spots during Superbowl XXXIX. The commercial featured WWE wrestler Candice Michelle experiencing a “Wardrobe Malfunction,” a clear parody of the half-time show fiasco involving Janet Jackson the previous year. After having 16 variations of the storyboard filmed and rejected by the Fox Network, version number 17 was pre-approved for broadcast during the first and fourth quarters of the game. The 30 second spot in the first quarter drove a web site traffic increase of 1,600% to the GoDaddy site, and then a strange thing happened: the commercial never played a second time. NFL executives purportedly pressured Fox to pull the commercial due to its “inappropriate” nature, despite the fact that it had already been paid for, pre-approved by Fox, and initially aired. Led by GoDaddy CEO Bob Parsons, the blogosphere screamed censorship like bloody murder, which only served to fuel additional publicity. In the end, GoDaddy deemed the event so successful that they now define their brand around the “GoDaddy Girls,” airing annual Super Bowl commercials that tiptoe along the edge of broadcast acceptability.

At the center of the GoDaddy controversy is the correlation between advertising and brand identity. As a content provider, the Fox Network understands that their brand will be held responsible for the quality of both the program content and the advertising they deliver. If either aspect of the broadcast is sufficiently offensive or inept, they risk losing viewers to other stations. Consequently, Fox must provide content that is tame enough to avoid outrage from extremely conservative viewers while remaining provocative enough to satisfy the desire of third party companies seeking to push the envelope with their ad strategy. Content providers in any medium will be judged by the quality of the content they provide, and that includes the use and placement of advertising. This can be a tough balancing act, and Fox isn’t alone in walking the tightrope.

When it comes to the Web, the importance of managing advertising content takes on a new dimension. Hackers are increasingly using fraud and social engineering tactics to infiltrate advertising networks, and then utilizing their position within this circle of trust to inject malware, browser redirects, and cross site scripting attacks on unsuspecting visitors. If these attacks are successfully executed, hackers may steal credit cards, social security numbers, banking information, personal photos and anything else that has been digitized on the victim’s computer. Alternatively, a visitor’s computer may be turned into one of many “sleeper cell agents” in a botnet, ready to respond to a few keystrokes at any time and become an active participant in a worldwide Internet attack. It isn’t just web site visitors who are vulnerable. This same strategy can be used by black hat marketing consultants to siphon traffic from one web site to a competing web site or even to blacklist an entire site from the Google search index. The worst part? Hackers are able to target their attacks with profound granularity, making it extremely difficult for anyone within the targeted organization to know the attack is even happening.

The risk posed by vulnerable advertising mediums is not merely theoretical. In 2009, I documented two separate exploits that successfully penetrated highly trafficked and popular web sites. Both sites had full time IT teams who were previously unaware that the exploit was occurring. Furthermore, in a now highly publicized event in September of 2009, the New York Times was the victim of a malware advertiser who legitimately purchased ad space from the Times while pretending to be a representative of Vonage. IT departments and technical staff are trained to watch site visitors for malicious activity, but painfully few are watching the advertisers.

Deconstructing the Hack

Client-side arbitrary code execution is the primary culprit behind advertising based attacks. Attackers first gain trust with the target by posing as a legitimate advertiser. This process may be as simple as paying for space in an automated advertising system, or as involved as calling a major corporation while posing as a sales rep or marketing executive from another company. After the attacker has been approved as an advertiser, they develop a custom script to exploit the medium being used. They may start off displaying advertising that looks legitimate, but inevitably they switch to the malicious ad that begins to infect or otherwise manipulate site visitors.

Depending on the amount of freedom granted to an advertiser, a variety of techniques may be used to deliver the hacker’s payload. Many setups allow advertisers to automatically submit a combination of HTML, CSS and JavaScript code to be embedded within the layout of the publisher’s site. In this scenario, hackers can easily embed malicious scripts by using JavaScript or by including an external Flash SWF in the markup. In the off chance that this code is reviewed at all before publication, it is likely reviewed by someone in marketing or sales who is only examining the submission based on the content currently displayed and is unable to analyze the underlying code for potential security vulnerabilities.

Allowing advertisers to place custom Javascript or Flash files inline as part of a web site’s markup is especially dangerous as the advertiser is no longer restricted by cross-domain access policies. This leaves the advertiser with the power to do virtually anything the web site developers can do, such as posting AJAX requests or altering any element of the DOM. In an attempt to prevent this, some web sites have opted for an alternative setup that links an iframe or traditional frame to a server belonging to the advertiser. However, this approach is also flawed because changes to the advertising code may be made at anytime and the publishing site is powerless to implement a pre-approval process or apply any automated content filtering.

Regardless of the method utilized, if an attacker gains the ability to execute custom code on the target site, Pandora’s box has been opened and virtually all the evil of the Internet may be unleashed. A few fictional yet plausible exploit scenarios include the following:

You Won (Malware)!

Johann is a regular visitor to Finance Magazine’s web site. Like most Finance Magazine visitors, he is an investor with a diversified portfolio in mutual funds, bonds, and individual stocks. While browsing the latest financial news, a popup branded with the magazine logo suddenly appears and announces that he won a free 2 Year subscription to FM and a chance to win lunch with Warren Buffett. Lunches with Buffett are normally valued in the millions, and Johann has been wanting a print subscription to the magazine for some time. He clicks “Accept” and is asked to download the registration form. At first he is a bit suspicious and doesn’t understand why the registration form is a downloadable .exe file, but it is a company promotional from the official web site, so he reasons it must be okay. After downloading the application, he launches it and is asked several questions about his financial net worth. He is then asked for his full name, phone number, address, e-mail address and social security number. He is again a bit suspicious and doesn’t understand why he needs to enter his social security number, but the form does looks very professional. He clicks the info button next to the Social Security Number field and is shown this dialogue message:

You must enter your social security number in order to ensure that “Lunch With Warren” contest participants are limited to one entry per person.

With visions of the “Sage of Omaha” in his head and the promise of the next printed issue of Finance Magazine at his door step, Johann fills out the form and clicks submit.

Several months later, Johann’s financial life is in ruins. His personal information was used to register for several credit cards and a bank loan was issued for a Mercedes SLK in California. The executable file he downloaded included a custom Trojan Horse virus that allowed the attackers to login to his personal machine. They used this access to acquire his banking information and passwords, which they used four months later to wire over $10,000 to an account in the Cayman Islands. Although Johann is now suing for criminal negligence, his life (and his credit) will never be the same.

The Black Hat Who Stole Christmas

Brianna is a successful small business owner with an online niche retail store that averages $25,000 in sales and 500,000 visitors per month. In addition to a product catalog, her site also contains high quality articles and videos that pull traffic from Google and allow her to further monetize her online presence by selling custom advertising. Advertising is sold on a month-by-month contract basis, and advertising providers are given an account that they paste HTML, CSS, and JavaScript in so it can be included directly in the site markup. Usually, Brianna’s sales skyrocket for the entire month of December as Christmas approaches. This year, however, she has seen a 60% reduction in traffic and sales are plummeting. After closely analyzing her site analytics, she realizes that traffic from Google has drastically been reduced. She went from being in the top 10 results for her product niche to not appearing anywhere within the top 5 pages, and she can’t figure out why. What Brianna doesn’t realize is that she sold an advertising slot for December to a Black Hat SEO optimizer working for a competitor. As part of his overall strategy for propelling his client to the top, he decided to cut the legs out from underneath the competitors by running advertising templates on their sites that carefully and skillfully violated nearly every technical SEO guideline required by Google. Brianna made a few hundred dollars for the advertising space, but unknowingly violating Google’s SEO rules would cost her tens of thousands of dollars in the year ahead.

Defending Against Malicious Advertisers

Unfortunately, a foolproof technical solution to malicious advertisement doesn’t exist. However, this fact is not an excuse for apathy. The risk to both organizations and web site visitors can be mitigated by applying these technical steps:

  1. Preview Ad Submission

    Within your advertising process, a system should be setup to preview all advertising before it is published live. This process should minimally include the ability to preview the way an ad looks and functions, but ideally it will also involve a quick scan of the actual advertising code to check for any unusual pieces of content (e.g. a few lines of encrypted JavaScript). If ad provider’s can automatically update their content, they should be sure that each new version is also approved before publication.

    This tactic can not be used if ad placement is achieved by embedding frames or iframes that link directly to a third party server.

  2. Restrict Dynamic Advertising

    The single most effective method of preventing advertising abuse is to ban your advertisers from executing any dynamic advertising code. This process is as simple as stripping any scripting tags from advertising content and is extremely effective. However, the potency of this tactic comes at the cost of advertising flexibility as it limits all advertising to stylized images and text. In a medium where small games and other interactive content is often used to garner clicks and entertain eyeballs, this is often not a viable tactic. When scripting code is permitted, certain dynamic content should still be banned. For example, anything that involves alert() or document.location() calls in JavaScript could be stripped while leaving other code in place.

    This tactic can not be used if ad placement is achieved by embedding frames or iframes that link directly to a third party server.

  3. Sandbox Dynamic Advertising

    In scenarios where dynamic content is permitted, it is useful to place ads within frames or iframes to take advantage of cross-domain safety restrictions. Yet as we have seen, using these constructs to link directly to a third party server is a security vulnerability as advertisers can easily change the content displayed without providing the publishers an opportunity to review the changes or strip malicious code. To obtain the best of both worlds, create an advertising sandbox by designating a domain or subdomain specifically to serve advertising content. Then place frames or iframes on your main site that link directly to the new domain. Because you control the ad domain, you will be able to preview ad submission, restrict dynamic advertising, and benefit from the added security that cross-domain security restrictions provide.

Even when implementing the safeguards above, the decision to grant an advertiser space on your web site should not be taken lightly. Doing so inherently confers a degree of trust upon a third party. Ensure that trust is well placed by implementing a screening policy for all new advertising sign ups. Such a policy could be as simple as calling companies directly to verify that the representative is authorized to sell advertising on their behalf or as involved as requiring all advertisers to provide copies of their business incorporation license or other government issued identification. Regardless, the threat can not be delegated to the IT staff and forgotten. Marketing and sales play an equally important role, and the safest organizations are those who view security as the shared responsibility of all the members within it.

There was a time when good advertising meant entertaining video or amusing copy. It could be judged purely on face value and the ability to generate ROI. That time has passed. In an increasingly interactive world, it is now more important than ever for organizations and individuals to understand that advertising consists of both form and function. Ignoring this fact can result in something far worse than assaulting the sensibilities of your audience; it can devastate their lives. Let content providers and audiences beware: the age of badvertising has begun.