What Is Browser Extension Security?
Browser extensions improve web browsers by adding features like productivity tools, ad blockers, and custom interfaces. While convenient, extensions also create a new avenue for potential security vulnerabilities.
Extension security focuses on identifying and mitigating risks related to malicious code, excessive permissions, and potential misuse of collected data. It is important given the widespread adoption of extensions across various browsers.
Many users install extensions without fully understanding their implications. A poorly designed or malicious extension can put personal data, browsing habits, and even devices at risk. Today’s browser ecosystems provide tools to address security concerns, but maintaining extension security requires vigilance from both developers and users.
This is part of a series of articles about browser security
In this article:
- Common Security Risks in Browser Extensions
- How Big Is the Problem? Malware in Google’s Chrome Web Store
- 5 Best Practices for Secure Use of Browser Extensions
Common Security Risks in Browser Extensions
Here are some of the main security risks that arise when using browser extensions.
1. Malware and Malicious Code in Extensions
Malicious extensions often mimic legitimate tools to deceive users into installing them. Once installed, they can inject JavaScript into webpages, monitor user activity, and exfiltrate sensitive data like passwords, authentication tokens, and credit card details. Some even install secondary malware or create persistent backdoors on the user’s device.
These extensions may use techniques like obfuscation, delayed activation, or environment checks to avoid detection during the browser store review process. Some are programmed to activate only under certain conditions, making them harder to identify. Because browser extensions run with privileges within the browser’s context, they have the power to manipulate web pages, intercept API calls, and bypass traditional security boundaries.
2. Data Privacy Concerns and Leaks
Extensions often need access to user data to function, but this access can be abused. For instance, an extension that manages bookmarks or browser tabs might also access full browsing history and all data entered on websites. If such data is transmitted to remote servers, either for analytics or monetization, it becomes a privacy liability.
Worse, many users remain unaware of the data being collected. Some extensions operate under vague or misleading privacy policies, while others include third-party code that sends data to advertisers or analytics providers without the user’s knowledge.
Even non-malicious developers might introduce vulnerabilities that lead to data leaks. For example, insecure API endpoints, insufficient encryption, or poorly configured cross-origin resource sharing (CORS) policies can expose data to unauthorized actors.
3. Risks from Over-Permissioned Extensions
When an extension requests permissions that go beyond its advertised purpose, it increases the risk surface dramatically. For example, a note-taking extension might request the ability to read and change all data on all websites, which is not needed for its primary function.
These excessive permissions can be exploited if the extension is compromised or if the developer decides to misuse them. The broader the access, the more potential damage an attacker can inflict, from reading emails to performing unauthorized actions on behalf of the user.
4. Supply Chain Attacks via Extensions
Supply chain attacks target the development or distribution lifecycle of browser extensions. These can occur when attackers gain access to a developer’s account, compromise build tools, or exploit flaws in automatic update systems. Once the attacker controls the extension, they can silently distribute malicious updates to all existing users.
One common scenario involves purchasing a popular but no longer maintained extension. The attacker then publishes a new version with hidden malicious code. Because the extension is already installed and trusted, users receive the update automatically, without suspecting foul play.
5. Legitimate Extensions Turning Malicious
Sometimes, a well-known and widely used extension becomes malicious over time. This usually happens after ownership changes hands, often without the user being notified. The new owner may insert advertising scripts, tracking pixels, or more dangerous payloads into the extension code.
These changes may be subtle—like injecting affiliate links or displaying ads—or more serious, such as harvesting personal information or enabling phishing attacks. Because updates are pushed silently through the browser’s auto-update mechanism, users rarely notice when the behavior of an extension changes.
Related content: Read our guide to secure browser extension (coming soon)
How Big Is the Problem? Malware in Google’s Chrome Web Store
Despite public assurances from Google, recent data reveals significant gaps in the safety of browser extensions hosted on the Chrome Web Store.
In a 2024 blog post, Google’s Chrome Security Team stated that less than 1% of all installs from the store included malware. However, this still means that potentially 1 in every 100 installations could harm users—a risk level that would be unacceptable in most other industries.
A recent Stanford University study evaluated extension safety in the Chrome Web Store and identified thousands of “security-noteworthy extensions” (SNEs)—extensions containing malware, violating privacy policies, or with known vulnerabilities. Alarmingly, these risky extensions often remain available for years, accumulating millions of installs. Over three years, more than 346 million users installed such extensions.
The study highlighted several systemic problems:
- User ratings were found to be unreliable indicators of safety, as dangerous extensions frequently maintained high ratings.
- A majority of extensions—nearly 60%—had never received an update, leaving them vulnerable to known exploits and missing security improvements like those introduced in Chrome’s Manifest V3 platform.
- Even among extensions that were actively maintained, developers often failed to patch vulnerable JavaScript libraries. Nearly 40,000 extensions used such libraries, impacting around 500 million users.
- 42% of extensions known to have vulnerabilities remained live and exploitable two years after disclosure.
Together, these findings demonstrate that extension security issues go far beyond isolated incidents of malware. They point to persistent structural weaknesses in browser extension ecosystems, where outdated code, unpatched libraries, and insufficient review processes put hundreds of millions of users at ongoing risk.
5 Best Practices for Secure Use of Browser Extensions
Here are some of the ways that organizations can ensure greater security when using browser extensions.
1. Regularly Reviewing and Updating Extensions
Browser extensions often run with broad privileges, and even a single outdated or abandoned extension can become a vector for attack. Users should perform regular audits—at least quarterly—of all installed extensions. This includes checking whether each extension is still necessary and verifying that it is being actively maintained by the developer.
Look for signs of abandonment, such as missing recent updates, broken functionality, or removal from official extension stores. If an extension has not been updated in a long time, especially in response to known security issues, it should be removed.
Users should also ensure auto-updates are enabled and functioning. However, updates should not be blindly trusted—users should inspect changelogs, permissions, and recent user feedback to detect suspicious changes in behavior, especially after ownership transfers or major version changes.
2. Minimizing Extension Use to Essential Functions
Every installed extension increases the potential for compromise. Many users accumulate dozens of extensions over time without reassessing their relevance. Each extension—whether benign or not—has the ability to impact browser performance, access sensitive data, or introduce exploitable bugs.
Users should adopt a minimalist approach, keeping only those extensions that are critical to their tasks. For example, instead of having separate extensions for screenshots, annotations, and sharing, one multifunctional, well-reviewed extension might suffice. Users should also avoid novelty extensions or those that offer marginal utility relative to the risk they present.
By reducing the number of active extensions, users limit the number of permissions granted and simplify security management. Less complexity makes it easier to spot anomalies and maintain a more secure browsing environment.
3. Using Separate Browser Profiles for Sensitive Tasks
Creating isolated browser profiles helps contain the reach of potentially compromised extensions. Sensitive activities—such as online banking, access to company portals, or handling confidential documents—should be conducted in a clean profile with no extensions or with only those that are security-vetted.
This separation acts as a boundary: if an extension in a general-use profile is compromised, it cannot affect sessions, cookies, or data in the secure profile. Browsers like Chrome, Edge, and Firefox support multiple profiles and allow users to quickly switch between them.
In corporate environments, IT teams can enforce these divisions by using managed browser configurations. For individual users, setting clear rules about which tasks are performed in which profile can substantially reduce exposure.
4. Implementing Extension Allowlisting and Denylisting
Organizations, especially those with many employees or contractors, must proactively manage which extensions can be installed. This involves creating allowlists of approved extensions that meet internal security, privacy, and functionality standards, as well as denylists that block known malicious or non-compliant ones.
Enterprise tools like Chrome Enterprise and Microsoft Edge for Business allow administrators to enforce these policies via Group Policy Objects (GPOs) or management consoles. These tools can prevent users from installing non-approved extensions and alert administrators to policy violations.
This practice helps protect the organization from shadow IT risks, where users install extensions without oversight. It also helps enforce the principle of least privilege by narrowing the scope of tools running in users’ browsers to those that have been vetted and authorized.
5. Adopting Robust Browser Security Solutions
Organizations can enhance browser extension security without requiring users to change their preferred browser by deploying third-party browser security platforms. While some solutions require users to switch to a dedicated enterprise browser, which can hurt productivity and cause user dissatisfaction, other solutions provide a secure experience with a familiar browser environment.
These platforms integrate directly into existing browsers and provide advanced visibility, control, and threat detection capabilities. Advanced solutions provide real-time extension monitoring, anomaly detection, and policy enforcement—allowing security teams to audit all browser activity and block high-risk behaviors or extensions automatically.
Additionally, many of these tools support extension reputation scoring, enabling security teams to identify and block extensions with a history of malicious behavior, excessive permissions, or code vulnerabilities. By using browser-native APIs and lightweight agents, these platforms can provide robust protection with minimal performance overhead or user disruption. This allows organizations to support productivity while still enforcing a secure browsing experience.
Browser Extension Security with Seraphic
Browser extensions represent a significant and often overlooked attack vector in enterprise environments, with malicious or compromised extensions capable of accessing sensitive data, monitoring user activity, and serving as gateways for advanced persistent threats. While traditional security solutions struggle to monitor and control extension behavior due to their deep integration with browser functionality, Seraphic’s remote browser isolation architecture provides a comprehensive solution to extension-based risks. By executing all browser activity, including extensions, within secure cloud containers, Seraphic ensures that even malicious extensions cannot access corporate networks, steal sensitive data, or compromise endpoint security.
The challenge with extension security extends beyond obviously malicious add-ons to include legitimate extensions that may be compromised, overprivileged, or poorly coded. Extensions often request broad permissions that allow them to read and modify web page content, access browsing history, and interact with web applications, creating substantial security exposure that can be exploited by attackers. Seraphic’s isolation model contains these risks by preventing extensions from accessing anything beyond the isolated browsing environment, effectively neutralizing their ability to exfiltrate data or establish persistence on corporate systems.
Seraphic’s approach to extension security includes:
- Complete extension isolation: All browser extensions execute within secure cloud containers, preventing them from accessing corporate endpoints, networks, or sensitive data, regardless of their permissions or intent.
- Risk-free extension usage: Employees can continue using productivity extensions and browser add-ons without security concerns, as all extension activity is contained within the isolated browsing environment.
- Transparent extension management: Organizations gain visibility into extension usage patterns and behaviors without requiring complex monitoring tools or policies that restrict user productivity.
- Zero-trust extension environment: Treats all extensions as potentially compromised, applying consistent isolation policies regardless of extension reputation, source, or apparent legitimacy.
- Elimination of extension-based attacks: Prevents common extension attack vectors, including data exfiltration, credential harvesting, session hijacking, and browser-based malware distribution.
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