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A Study of Clickjacking 2: Existing Defenses and New Attack Variants

Lin-Shung Huang now describes the current clickjacking defenses and outlines the new attack variants that were evaluated using the Amazon Mechanical Turk.

Existing Defences

Visual integrity protection

Visual integrity protection

So, I talked about the existing attacks. Now, what are the current defenses to protect visual integrity? One method is user confirmation. The idea is simple, just to ask the user again but, of course, it’s really annoying. Another idea is to randomize the sensitive UI so that it makes more difficult for attacker to correctly position the decoy button under the target. However, it’s not reliable since attackers may trick the users to perform multiple clicks, and eventually the attacker will succeed.

Framebusting is currently the standard defense against clickjacking. The idea is to disallow embedded or framed objects and cause the browser to render an error frame. Unfortunately, this is incompatible with third-party objects such as Facebook’s ‘Like’ button. And also browsers can adopt an opaque overlay policy that disallows transparency. However, it breaks existing sites.

Finally, there is a type of defense that allows embedded or framed objects and detects the visibility of the target object at that time of the user click. This is implemented in Firefox extension called NoScript however it often triggers false positives due to its on-by-default nature.

Temporal integrity protection

Temporal integrity protection

So, other existing defenses to protect temporal integrity. Well, one common approach is to impose a delay after displaying the UI, such that users have enough time to make an informed choice before performing the click. For example, when the users install an extension on Firefox, they are required to wait a few seconds before they are allowed to click. We think this is actually a good technique, although sometimes it may be annoying to the users. And at the time of study, none of the current defenses consider the integrity of pointers.

New Attack Variants

In the next section I’ll introduce our three new attack variants that can evade the existing defenses and cause severe damages such as accessing the user’s webcam, stealing the user’s email and revealing the user’s identity.

Attack evaluation methodology

Attack evaluation methodology

For each of the attacks I also want to show you how effective they are. So, for evaluating the effectiveness we recruited roughly 2000 web users on Amazon Mechanical Turk, we offered 25 cents per user only allowing each user to participate once, and only for one treatment.

Attack involving user’s webcam access

Attack involving user’s webcam access

1 In the first attack the attacker presents an interstitial video ad to the user (see right-hand image). Users can either watch the ad for 60 seconds or click to ‘Skip this ad’. So, now I want to ask all of you a question, please, raise your hand if you would watch the ad for 60 seconds… Thanks.

So in our study we actually observed that 51% of users skipped the ad. So, suppose the user moves the cursor over to the ‘Skip Ad’ link and clicks. How many of you noticed that the real cursor was hidden all the time and now the cursor is on the ‘Allow’ webcam access button.

Our study shows that 43% of the users fell for the attack, and if you think about it this is quite serious – getting webcam access to over 40% users is actually really bad. And if we consider that 51% of the users tried to skip the ad, that’s over 84% success rate on those users. And note that in this attack temporal integrity is preserved, no Pay-and-Switch techniques were used, however, the visual integrity of the pointer isn’t preserved.

Accessing user’s email account

Accessing user’s email account

2 In the second attack the attacker asks the user to double-click a blue button on the page. When the user clicks on the button the attacker yields the screen real state to the Google auth dialog in the pop-up window, and the second click goes to that dialog (see left-hand image).

As a result, the attacker was granted access to the user’s Google account. We found that 47% of the users fell for this attack and, again, this is extremely serious as almost half of the users’ emails would have been accessed. Note that this attack works even though Google deploys framebusting defense.

Revealing user’s identity

Revealing user’s identity

3 In the third attack the user is asked to play whack-a-mole game. We encouraged users to click on a sequence of buttons as fast as possible (see right-hand image). From the beginning the real cursor is hidden and the user is tricked to control a fake cursor. So, after the user has successfully clicked on several buttons, a Facebook ‘Like’ button is repositioned under the user’s real pointer and which users may not notice while clicking.

The attack combines cursors spoofing and fast-paced clicking techniques and was the most effective attack that we have; we found that 98% of users fell for it. So, once the user clicks on the ‘Like’ button the attacker can instantly reveal the user’s identity, we described how this is done in our paper.
 

Read previous: Clickjacking: Attacks and Defenses

Read next: A Study of Clickjacking 3: Ensuring Visual and Temporal Integrity

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