Understanding Browser Extensions and Their Risks

Introduction to browser extensions

Imagine you sit down at your computer to catch up on work. As you open your web browser, several pop-up ads appear, which you close one-by-one. A quick look at your personal email reveals an appointment reminder that needs to be added to your work calendar. You also see a promotional email from your favorite brand about a flash sale. Before distractions take over, you set a timer on your phone for one hour—dedicating this focused period to your original task before diving into personal or leisure activities.

Now imagine if instead of taking all those actions manually, you had a digital assistant or two to help you. Someone to filter out all the ads, another person to automatically sync meetings to your calendar, and one to even block distractions so you can focus on high priority tasks.

Most people might not be able to hire an assistant, so they look at alternative solutions like browser extensions—a small software module that enhances and personalizes the functionality of web browsers.   While it’s common for users to install browser extensions to tailor their online experience to better meet their needs and preferences, these tools also carry significant security risks. Browser extensions are yet another avenue that can be exploited by cyber attackers or act as a vehicle for malware.

This post examines the dual role of browser extensions as a productivity enhancer and security risk. Our experts also outline steps organizations can take to help employees use legitimate browser extensions safely and effectively.

What are browser extensions?

Browser extensions—sometimes referred to as plug-ins or add-ons—are small software modules that enhance and personalize the functionality of web browsers, such as Chrome, Firefox, Edge, and Safari. Users install these tools to tailor their browsing experience to better meet their needs and preferences and enhance the functionality of the website.

Some common tasks that browser extensions can perform include:

• Blocking and filtering pop-up ads or dynamic content
• Saving and protecting passwords
• Tracking or limiting the amount of time spent on designated websites or applications
• Checking and correcting spelling, grammar and other writing issues
• Enhancing accessibility and inclusivity with assistive features

As illustrated in the list above, browser extensions can be additive or limiting—meaning they can enhance the experience by adding new features, such as providing alternative text (alt text) to describe an image to improve accessibility, or removing other elements, such as blocking pop-up ads or auto-play for online videos.  

Now with the advent of generative AI, browser extensions are also evolving to become full-on AI assistants, an advanced type of tool that can often gather and analyze browser data to automate tasks, offer recommendations, or raise alerts.

Risks associated with browser extensions

While browser extensions can be a useful tool for web users, they also create a significant set of security risks. Think of a browser extension as a door—on one hand it opens the user to a world of new possibilities; on the other, it can also serve as a gateway to exploits.

While legitimate extensions often need considerable permissions to function properly, some request more access than what is truly needed. These permissions can be exploited, granting malicious actors access to sensitive data and confidential information, including web traffic, saved credentials, session cookies and clipboard data.

This valuable data can then be leveraged for malicious purposes or sold for profit. For instance, attackers may use the obtained credentials to carry out identity-based attacks or support convincing phishing schemes.

For example, according to CrowdStrike researchers, attackers behind the Kiron malware family weaponized browser extensions in 2024 to exfiltrate sensitive user data, such as email addresses and browser cookies. The extensions, embedded as encrypted ZIP files within the malware's core, included scripts to scan webpages for email addresses and monitor webmail tabs to steal cookies, which were then exfiltrated to command-and-control servers. These stolen credentials allowed attackers to hijack accounts or perform further exploitation.

Additionally, because extensions are integrated directly into browser applications and don’t generate process start events, security issues can be more difficult to detect compared to traditional desktop applications. This gap enables threat actors to “hide in plain sight,” carrying out harmful activities without detection for significant periods of time.

While excessive permissions in legitimate extensions is perhaps the most common browser extension risk, these tools can be programmed with harmful intentions and exploited to distribute malware.

CrowdStrike’s evaluation of browser extensions in our production environments reveals that well over half of extensions require what could be considered excessive permissions. These elevated permissions pose serious risks, potentially enabling malicious actors to monitor web traffic or alter browser tabs.

Identifying malicious browser extensions

Detecting malicious or problematic browser extensions can be challenging, especially for users unfamiliar with the complexities of software. However, certain tell-tale signs can help identify outright malicious or potentially harmful extensions. These include:

• Requesting unnecessary or invasive permissions: Malicious browser extensions often request more permissions than they need to function. Be on the lookout for extensions that request access to all browsing data or the ability to modify website content. This excessive access can allow attackers to capture sensitive information, monitor user activity, or inject malicious scripts into web pages.
• Inserting advertisements or tracking user behavior: Some malicious browser extensions manipulate user sessions by injecting unauthorized ads which can be used to track users’ online behavior. This not only disrupts the user experience but also compromises privacy, since collected data, including personal information and passwords, can be sold to third parties or used to advance cyberattacks.
• Redirecting users to untrusted websites: Extensions that redirect users to suspicious or untrusted websites can expose them to phishing attempts, malware downloads, or other cyber threats. This tactic is often used to generate ad revenue for attackers or to steal user credentials through fraudulent login pages.

6 Best practices for managing browser extensions

Effectively managing browser extensions is an essential part of the cybersecurity strategy. Implementing the following best practices can minimize the risks associated with extensions while still maximizing the advantages of these tools.

What are the best practices for managing browser extensions?

1. Limit the number of installed extensions

2. Download extensions from trusted sources

3. Monitor permissions

4. Keep extensions updated

5. Educate users on extension risks

6. Assess browser extensions security

1. Limit the number of installed extensions

More extensions equals more risk. To reduce the attack surface and limit potential vulnerabilities, users should install only essential browser extensions.

It is also important to regularly review and uninstall extensions that are no longer in use or whose functionality overlaps with another tool. This helps minimize any vulnerabilities that arise over time, as well as protect against advanced attack techniques.

For example, one popular tactic used by attackers is ownership takeover, which is when threat actors purchase or otherwise take over previously legitimate browser extensions that already have a user base and push out malicious updates to compromise target systems.

2. Download extensions from trusted sources

Users should remain vigilant when installing browser extensions, as malicious extensions often mimic reputable vendors by using similar names or branding. Others may capitalize on demand by marketing a tool with popular features at a lower cost.

To minimize risks, follow these steps:

• Download extensions only from official browser stores or trusted developers.
• Check user reviews and developer details to verify the extension’s authenticity.
• Assess the extension’s security protocols and carefully review requested permissions before installing.

When it comes to browser extensions, one of the most dangerous things a user can do is “sideloading.” This involves installing browser extensions from sources outside the official web store by directly adding the extension files. This method bypasses the usual safeguards that come with the browser stores. Attackers exploit this method by bundling malicious extensions with seemingly legitimate software applications. When users install these applications, the hidden extensions are also installed, granting attackers access to the users' browser and data.

3. Monitor extension permissions

Excessive permissions are a red flag for potentially malicious browser extensions, but they can also pose risks even with legitimate ones. Permissions such as access to all website data, clipboard content, or browser history may exceed what is necessary for the extension's intended functionality. These permissions could expose sensitive information or be exploited if the extension is compromised.

To mitigate risks, always review the permissions requested during installation to ensure they are essential for the extension’s purpose. It’s important to note that even when downloading extensions from a web store, these tools can sometimes expand their permissions upon installation and/or download additional malicious payloads. This is a popular obfuscation tactic where adversaries publish extensions to web stores with minimal initial permission requirements but expand their footprint with harmful intentions.

Users should revoke permissions for extensions that request unnecessary access to sensitive data without a clear justification. When in doubt, consult your IT support team to assess whether the tool is safe to use and, if not, explore secure alternatives.

Remember: there are hundreds of thousands of browser extensions on the market, many of which serve similar purposes. If one tool does not meet your security and privacy preferences, it may be possible to find a reputable alternative that offers the same features with added security.

4. Keep extensions updated

Many cyberattacks stem from unpatched software vulnerabilities. While security teams often focus on operating systems and major application updates, browser extensions are frequently overlooked despite carrying significant risk.

To mitigate this risk, enable automatic updates or manually update extensions to ensure they include the latest security patches. Additionally, remove extensions that are no longer supported or maintained by developers, as outdated software becomes increasingly vulnerable over time.

5. Educate users on extension risks

Prevention starts with education. Organizations can safeguard their assets, operations, and customers by implementing robust security training for all employees.

This training should include guidance on identifying potentially malicious extensions, such as those with poor reviews or unknown developers. It should also include a lesson on how to check the permissions of the extension and what qualifies as “excessive permissions.” Employees should also be taught to recognize suspicious behaviors, such as extensions redirecting to untrusted websites, prompting additional downloads, or attempting to alter application settings.

Beyond warning signs, employees should gain a clear understanding of the data privacy risks associated with poorly vetted or malicious extensions. For instance, demonstrating how a browser extension might capture and store a password for one application—potentially enabling hackers to exploit this data for unauthorized access to other accounts, such as email or banking platforms—can illustrate the severity of these risks to both the individual and the organization.

6. Assess browser extensions for security

Assessing the security of browser extensions is a critical step for both individuals and organizations in safeguarding their digital activity and assets. Since even legitimate browser extensions can also introduce significant risks, it is important to conduct a multi-faceted browser extension assessment to limit risk both when downloading a new extension and using an existing one.

A robust browser extension assessment must review permissions requested by extensions. Whether you are installing a new browser extension or using an existing one, it is important to carefully review the permissions requested by each extension. Permissions should align with the intended functionality of the extension and be limited only to the data needed to perform that specified task. Remember that excessive permissions are an important warning sign—be it a red flag for a legitimate extension or a tell-tale sign of a malicious one.

Assessing the security of browser extensions is often a complex and time-intensive task, yet it is vital for safeguarding digital environments. Traditional security tools may fail to detect vulnerabilities in legitimate browser extensions, leaving organizations exposed to potential threats.

Given these challenges, engaging a reputable third-party vendor to conduct a comprehensive browser extension assessment can be an ideal solution. Such experts bring specialized tools and knowledge, enabling businesses to identify and address vulnerabilities effectively while also allowing teams to make use of the benefits of these tools.

Securing browser extensions with CrowdStrike Falcon® Exposure Management

CrowdStrike Falcon® Exposure Management, is a comprehensive, proactive security offering that helps organizations manage and mitigate risks related to browser extensions.

Falcon® Exposure Management contains a Browser Extension Assessment feature, which allows security teams to:

• Identify and assess security risks associated with browser extensions
• Monitor and evaluate extensions across an enterprise to help maintain alignment with compliance frameworks (i.e. GDPR, SOC2, etc) and security policies
• Take swift action against malicious or non-compliant extensions to safeguard the organization

With CrowdStrike Falcon® Exposure Management, security teams don’t react—they take control with proactive security. This solution, and its supporting features and assessments, enable a centralized approach to exposure management, empowering businesses to enhance productivity without compromising security.