Scheme Flooding Vulnerability- A Threat To Online Privacy

Iam Waqas
Published 09/02/2021
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Online anonymity has slowly and surely ceased to exist as cyber attacks’ sophistication continues to grow at an overwhelming rate. Amidst this, a common ground for data breaches that is often ignored is browser vulnerabilities. Although our web browsers play a significant role in creating our online presence, browser vulnerabilities are often neglected and overlooked as insignificant, allowing cybercriminals a somewhat of a defenseless area to exploit.

When it comes to attaining browser privacy, the utmost care we implement is merely using a few ad-blockers to stop the influx of annoying ad pop-ups. Otherwise, browser privacy is a massively neglected issue which is why vulnerabilities like scheme flooding are rapidly emerging and sneakily becoming a reason for data breaches and other privacy exploits.


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What is scheme flooding vulnerability?

Present from the last five years, scheme flooding vulnerability is a security flaw within web browsers allowing websites to track their users across different desktop browsers. By monitoring and collecting private information, website owners can link identities together and create a personality profile of individual users.

The vulnerability has gained its name as “scheme flooding” primarily because it exploits all browsers’ custom URL schemes as an attack vector. The custom URL scheme helps the vulnerability to create unique identifiers based on the information installed within your device. The identifier is further used to keep a continuous track of user activity through every web browser they use within that particular device.

So far, this vulnerability is present in all the web browsers widely available such as Chrome, Safari, and even Bing. However, the scheme flooding vulnerability within Tor is shocking as the browser has long since held the reputation of providing utmost online privacy. Despite its flaws, the Tor browser has been a renowned privacy tool, but it seems the scheme flooding vulnerability might deanonymize Tor altogether.


How does the scheme flooding vulnerability work?

In a nutshell, as mentioned above the scheme flooding vulnerability exploits custom URLs to build identifiers that helps identify users across browsers. However, there is a lot more complexity involved in the process altogether. To fully execute this vulnerability, an attacker has to go through the following steps necessarily:

  • Step 1: The attacker has to test devices for popular applications to create a specific identifier. For that, the attacker will have to compile a list of application URL schemes for testing. An attacker might create this list as per his goal, such as he might look for particular interest-based applications to target specific users.
  • Step 2: Create a goal-based website that can be used as a base for embedding the script. Like the list, the website can also be goal-based. If an attacker is targeting users having applications of specific interest, the website might align with that interest to lure a vast pool of possible victims.
  • Step 3:Once the target application list is created, the attacker has to proceed with integrating s script within websites that will test applications from the list within user devices. The script creates ordered boolean values, each marked “true” if the application is present and “false” if the application isn’t installed within the user’s device.
  • Step 4: The attacker proceeds using the boolean array to generate a permanent cross-browser identifier for individual users. The attacker might also embed the website with machine learning algorithms designed to guess the victim’s interest, occupation, and age using the installed applications within his device to ensure accurate results.

The custom URL is used as an attack vector since it has a record of every application available on your device, primarily as apps register their custom schemes within it.



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How does it exploit user privacy?

The scheme flooding vulnerability makes it vulnerable to privacy and security issues. Since it exploits a default feature within your browsers, it allows every threat actor to exploit user privacy. Users may have to face issues such as a total absence of browser privacy.

Browser privacy has previously been hard to achieve and requires multiple tools and settings to attain it. With scheme flooding vulnerability in place, attaining browser anonymity is complex since the threat actors create a stable and unique identifier to link user identities.

Even if a user manages to tune one particular browser for utmost online anonymity, any other browser used by the victim can cause privacy breaches. Most people only used Tor to carry out private use while keeping common browsers like Google, Safari, or Firefox for work use. The scheme-flooding vulnerability will also deanonymize Tor by linking all the browser identities together through the unique identifier.

A primary security concern with the identifier is that the applications used for identification can reveal personal information such as your occupation, habits, likes/dislikes, routines, and even your close friends and family. For example, attackers can use this vulnerability to spy on military and state secrets through apps and browser activity that should remain anonymous. One other concern with scheme flooding vulnerability is that users fall victim to target advertising and profiling.


How to ensure Privacy with Scheme Flooding Vulnerability?

Although the scheme flooding vulnerability has been around for almost five years, a little-known staunch method is available for mitigating it. As it relies upon on-device applications to create the unique identifier, VPNs and other browser privacy methods or even changing browsers do not help mitigate it.

Many researchers have merely said that the only possible way of gaining security from the scheme flooding vulnerability is when browsers have patched it. Till then, most recommend using CORS policies and browser window features as an effective method of mitigating it.

However, this method is hard to implement, and only the utmost tech-savvy users can implement it. Therefore the people of Reddit recommend a more straightforward process that involves using VMs and turning off JavaScript.

By turning off JavaScript, users can successfully enable script blocking and disabling the custom URL functioning. Apart from that, using VMs can also be a reliable solution. VMs or Virtual Machines allow working in an isolated environment that runs separately within your device through virtual components. With running browsers within a VM devoid of personal information or personally identifying applications, hackers won’t be able to create the unique identifier necessary for exploiting the scheme flooding vulnerability.

So far, using VMs might be the most reliable method to mitigate the scheme flooding vulnerability. Since it impacts each browser differently, the best way to ensure privacy and anonymity is to carry out browser activity within isolated environments with no personal information access.


Final words

Browser vulnerabilities are a popular way for attackers to exploit user data, so it is crucial to implement certain browning practices. Moreover, it is also critical to use the latest updated browsers to quickly recognize and pat patch security vulnerabilities such as the Tor browser.