Browser extensions are one of the most popular ways to customize and enhance our web browsing experience. Research firm Statista estimates that over 50% of internet users have at least one browser extension installed, with the most popular Chrome extensions reaching tens of millions of active users each. There are over 250,000 extensions available across the major browser marketplaces.
But this massive popularity also makes extensions an attractive target for cybercriminals looking to steal user data and infect devices with malware. As a cyber security professional who has specialized in protecting cloud data for over a decade, I‘ve unfortunately seen the dark side of browser extensions firsthand.
In this deep dive, I‘ll share my expert perspective on the real security risks that extensions can pose and what you need to know to stay safe in 2024 and beyond. I‘ll cover everything from key threats to practical tips for vetting extensions to thoughts on the future of add-on security as browsers evolve. By the end, you‘ll have the knowledge you need to harness the power of extensions without putting your data and devices at risk.
The Prevalence of Browser Extensions
First, let‘s take a look at some key statistics that illustrate just how widespread and important extensions have become:
- Over 50% of internet users have at least one browser extension installed (Statista)
- The Chrome Web Store hosts over 150,000 extensions and sees billions of weekly installs (Google)
- The top Chrome extensions have over 10 million weekly active users each (Extension Monitor)
- Firefox lists over 20,000 extensions in its official Add-ons site (Mozilla)
- Microsoft Edge has a library of over 4,000 add-ons (Microsoft)
Clearly, extensions are an integral part of the web experience for the majority of users. They allow us to block ads, manage passwords, customize site appearance, compare prices while shopping, check grammar, and so much more.
For many users, imagining browsing without their favorite extensions is difficult. However, this vast level of adoption also means that any security issues in the extensions ecosystem can have massive consequences.
The Security Risks of Browser Extensions
So what exactly are the risks posed by browser extensions? While not all add-ons are dangerous, there are several key ways that bad extensions can harm users:
1. Malicious Code and Malware
Perhaps the most obvious risk is that an extension may contain intentionally malicious code designed to steal data or infect systems. A 2021 study by researchers at the University of Maryland found that roughly 5% of Chrome extensions and 7% of Firefox extensions contained suspicious code snippets associated with malware.
Malicious extensions can take advantage of the powerful browser APIs and permissions to execute damaging payloads. For example:
- Keyloggers that record everything you type, including passwords and credit card numbers
- Spyware that monitors your browsing activity and exfiltrates sensitive data
- Adware that injects invasive ads into web pages or redirects your searches
- Botnet clients that enslave your device in a network of hacked machines
- Ransomware that encrypts your files and demands payment
- Crypto miners that hijack your CPU and electricity to mine digital currency
In many cases, malicious extensions will pose as legitimate, popular add-ons to trick users into installing them. Fake versions of extensions like AdBlock, Grammarly and The Great Suspender have infected tens of thousands of users.
2. Abusing Access Permissions
Even extensions that aren‘t outright malware can still abuse their access permissions to collect and expose user data in unethical ways. When you install an extension, it will request certain permissions to perform its functions – things like accessing browser storage, reading page content, modifying HTTP headers, etc.
For example, an ad blocker reasonably needs permission to modify page content in order to function. However, a different extension with that same permission could use it to steal data from the pages you visit. A 2019 study found that 4% of Chrome extensions used their permissions to collect and exfiltrate user browsing history.
Many users haphazardly click through permission prompts without much scrutiny. But these extremely broad permissions can easily enable unscrupulous developers to surveil your online activity for invasive tracking and advertising. Your data may be packaged up and sold to the highest bidder.
3. Introducing Vulnerabilities
Even extensions created with good intentions can inadvertently introduce new attack vectors and vulnerabilities if they are poorly coded or not properly secured. Any third-party code added to your browser inherently expands the potential attack surface.
For example, a 2020 report by cybersecurity firm Imperva found critical vulnerabilities in over 75% of the browser extensions they analyzed. These included server misconfigurations, insecure communication, CSRF flaws, authorization bypasses and more. Hackers can exploit these weaknesses to inject malicious code, steal data and escalate privileges.
Many extension developers are small teams or solo coders without rigorous security practices. A study found that 85% of Chrome extensions did not have a published privacy policy. Without regular security audits and stringent code review, it‘s all too easy for vulnerabilities to slip through the cracks.
4. Hijacking and Supply Chain Attacks
Even if an extension is initially created by a trustworthy developer, there‘s still the risk that it could be hijacked or compromised later on. Attackers may seek to purchase popular extensions from their creators in order to slip in malicious code in a future update.
This type of "supply chain attack" can be extremely difficult for end users to detect, since the extension comes from a previously trusted source. In a disturbing example from 2020, a popular Chrome extension called The Great Suspender, used by over 2 million people, was hijacked to spread malware before Google removed it from the Web Store.
There‘s also the possibility of a developer‘s account being hacked due to reused or weak passwords. The attacker could push a malicious update to the extension without the developer knowing. Two-factor authentication and strong password practices are critical for extension developers.
Real-World Impact of Malicious Extensions
To illustrate the scale of damage that malicious browser extensions can inflict, let‘s look at a few real-world examples of major security incidents:
- In 2020, 3 million users were impacted by a Chrome and Firefox extension breach that hijacked traffic and stole credentials (Avast)
- In 2019, 4 million Chrome users had their browsing history exfiltrated by a cluster of malicious extensions posing as utilities (Awake Security)
- In 2018, a malicious Chrome extension called MEGA was used to steal login credentials and crypto wallet keys from over 1.7 million users (Chainalysis)
- In 2017, a popular extension called Web Developer was bought and modified to inject ads in millions of users‘ browsers (Tripwire)
These incidents illustrate that the risks posed by extensions are not just theoretical. Real users are suffering real financial losses, data exposure and device infections every day due to malicious add-ons.
No user or organization is immune. In 2022, security firm Icebrg discovered an "extension botnet" that specifically targeted employees at Fortune 1000 companies, using their devices to commit ad fraud. Businesses need clear extension usage policies.
How to Tell if an Extension is Safe
With all of these risks, how can you determine whether a given browser extension is legitimate and trustworthy? Here are some key steps I recommend based on my years of experience in cybersecurity:
1. Stick to Official Extension Stores
One of the most important rules is to only download extensions from the official extension gallery for your browser (e.g. Chrome Web Store, Firefox Add-ons, Microsoft Edge Add-ons). All major browsers have one. While not perfect, these official repositories have stricter security checks and vetting processes than some random website.
For example, the Chrome Web Store prohibits extensions that abuse permissions, impersonate other extensions, spread malware, or engage in deceptive practices. Google does automated and manual reviews of each extension before allowing it in the store.
Of course, malicious extensions can still slip through (like The Great Suspender incident), but your odds are far better in the official stores. Avoid third-party sites offering extensions. If you find an extension somewhere other than the official gallery, be very suspicious.
2. Look at the Developer‘s Reputation
Before installing an extension, take a moment to research the developer behind it. Click through to their account page and see what other extensions they‘ve created. Are they a known, reputable company? Or a random individual with no information?
Check the reviews and ratings of their other extensions. Have people reported issues with data privacy, security or excessive permissions? Legitimate businesses tend to have a professional online presence with clear contact info. Solo developers should ideally have a public GitHub account showing their coding activity.
Be cautious of brand new developers with zero track record or extensions that have no support site or documentation. Again, everyone starts somewhere, but more trust should be earned for full access to your browser.
3. Scrutinize Requested Permissions
When installing an extension, you‘ll see a prompt listing out all the permissions and data the extension wants access to. For example:
- "Read and change all your data on the websites you visit"
- "Read and change your browsing history"
- "Display notifications"
- "Manage your downloads"
- "Manage your apps, extensions and themes"
While scary-sounding, many extensions need broad permissions to deliver their core functionality. An ad-blocker reasonably needs access to web page content. A download manager needs access to your downloads.
However, if a simple extension is asking for permissions that seem unrelated to its advertised purpose, that‘s a major red flag. For example, there‘s no good reason for a custom mouse cursor extension to access all your browsing history.
Before hitting accept, ask yourself if the permissions make sense for what the extension claims to do. When in doubt, deny access. Many extensions will still work with reduced permissions.
4. Read Reviews Carefully
If an extension has been around for a while, reviews from other users can give you useful insights into its trustworthiness (or lack thereof). Don‘t just look at the overall rating, but actually read through the most recent reviews.
See if people mention issues like the extension not working as advertised, injecting ads, crashing the browser, or suspicious behavior. Obviously, no extension will be perfect, but if you see a consistent pattern of complaints around privacy, security or performance, steer clear.
At the same time, some malicious extensions try to flood their listing with fake 5-star reviews to lure people in. If you see tons of short, vague, repetitive reviews, that‘s a bad sign. Look for detailed feedback from real users.
5. Assess Update Frequency
Even if an extension starts out secure, it can become vulnerable over time if the developer stops maintaining it. An outdated, abandoned extension is a security liability as browsers and websites change.
Before installing, check the "last updated" date on the extension listing. Has it received any updates within the last 12 months? Or has it not been touched in 5 years? Regular updates are a positive sign that the developer is active and committed to fixing bugs.
Starting in 2024, Chrome will require all extensions to be updated at least once per year or risk being removed from the Web Store. Unmaintained extensions can accumulate security flaws.
Additional Security Best Practices
Beyond vetting each individual extension, here are some broader security hygiene tips I recommend for staying safe:
Keep Everything Updated
One of the most important habits is to keep your browser and all installed extensions updated to the latest available versions. Enable auto-updates in your browser settings. Developers frequently push out updates to patch known security vulnerabilities, so staying current is critical.
For example, in 2020 Google had to push an emergency update to Chrome to fix a zero-day flaw that was being actively exploited in the wild. Outdated installations were at risk.
Use Extensions Sparingly
The more extensions you have installed, the greater your attack surface and overall risk. Only keep extensions that you truly need and use regularly. Audit your list every few months and clean out any unused ones.
Many users treat extensions like mobile apps, installing them on a whim to try out. But extensions typically have far more invasive permissions. The convenience isn‘t worth the added risk in most cases. Lean towards fewer extensions.
Use Open-Source Extensions Where Possible
While not feasible for every use case, choosing open-source extensions can be a good way to minimize risk. With open-source, the underlying code is publicly viewable on sites like GitHub. This allows cybersecurity researchers to audit the codebase and check for any suspicious behaviors.
Proprietary extensions can still be safe, but they are inherently a black box. You have to trust that the developer isn‘t doing anything shady behind the scenes. Open-source offers transparency and accountability.
Some good open-source extensions I recommend are uBlock Origin for ad-blocking, HTTPS Everywhere for encryption, and Privacy Badger for blocking trackers. They are developed by reputable non-profit groups like the Electronic Frontier Foundation.
Use Antivirus Software
No matter how careful you are, there‘s always some risk that a malicious extension could slip through your defenses. That‘s where antivirus software provides another important layer of protection. Antivirus programs include databases of known malicious extensions and can block them from installing.
Using an antivirus is especially important on Windows, which is the target of more malware overall. However, Mac and Linux users shouldn‘t assume they are immune. Antivirus is also important for detecting malicious extensions that may already be installed. I personally recommend Bitdefender, Norton 360, and TotalAV.
Extension Security Policies for Businesses
For companies and organizations, it‘s important to have clear policies around browser extensions to mitigate risks to sensitive corporate data. Here are some best practices I recommend:
- Maintain an allowlist of pre-approved extensions that employees can use. Restrict all others by default using endpoint management tools.
- Use browser management policies and group policy objects (GPOs) to control extension behavior across the organization.
- Prohibit extensions in incognito/private browsing mode, as this can bypass monitoring.
- Require employees to use a password manager extension for secure credential storage.
- Regularly review extension usage logs for anomalies and unknown extensions.
- Train employees on how to spot risky extension behaviors and the approval processes for installing extensions.
Having a defined policy and enforcing it with technical controls will go a long way towards minimizing extension-related incidents. Relying on individual employee discretion alone is not sufficient.
The Future of Extension Security
Looking ahead, the extension ecosystem is poised for a major transition to a new cross-browser technology called WebExtensions. This standard will allow developers to write extensions that are compatible with Chrome, Firefox, Edge, and Safari with minimal changes.
From a security perspective, WebExtensions are designed to be more modular and limited in scope compared to older extension APIs. Features like optional permissions aim to reduce over-privileged extensions. And the shift to service workers should provide better isolation between extensions and web pages.
However, WebExtensions won‘t be a silver bullet for extension security. Ensuring user safety will continue to require vigilance from browser vendors, security researchers, developers, and users alike. As browsers become more powerful, extensions will become more powerful in turn.
In the coming years, I expect we‘ll see browsers continue to tighten their extension policies and crack down on misbehaving extensions more proactively. Machine learning techniques will increasingly be used to detect anomalous extension behaviors.
Ultimately, the goal is to preserve the amazing potential of browser extensions to empower users while preventing them from being vectors for attackers.
Key Takeaways
Let‘s recap some of the key points from this deep dive:
- Browser extensions can introduce serious security and privacy risks if they contain malware, abuse permissions, or have unpatched vulnerabilities
- Vet extensions carefully before installing by sticking to official browsers stores, researching developer reputation, scrutinizing permissions, reading reviews, and assessing update frequency
- Minimize risk by using extensions sparingly, keeping them updated, leveraging open-source options, and using antivirus software
- Organizations need clear extension security policies and technical controls
- The WebExtensions transition may improve extension security, but vigilance is still required
No extension is 100% risk-free, but by following the guidance in this article, you can significantly reduce your odds of falling victim to a malicious one. Stay alert and proactive about what you let into your browser.
