Browser extensions have become deeply embedded in how millions of users interact with the web, offering valuable functionality from ad blocking and password management to productivity enhancement and content filtering. However, this widespread adoption has created a significant security challenge that remains largely underestimated by both individual users and many organizations. Research reveals that over 51 percent of all installed extensions present high security risks with the potential to cause extensive damage, while recent investigations have uncovered supply chain attacks affecting millions of users through compromised legitimate extensions. This comprehensive analysis examines the critical considerations users must understand before installing browser extensions, the sophisticated threats they face, and the methodologies necessary to conduct effective security vetting before granting these powerful tools access to personal and sensitive information.
Understanding the Browser Extension Security Landscape
The Nature and Scope of Browser Extensions
A browser extension represents a small software application designed to enhance the functionality of a web browser by adding new features, modifying user interface elements, or customizing how users interact with websites. Unlike traditional desktop applications, extensions receive special authorizations within the browser context that grant them access to sensitive data and browser operations. These applications are typically written in HTML, CSS, and JavaScript, and are made available through official web stores including the Chrome Web Store, Mozilla Firefox Add-ons, Microsoft Edge Add-ons, and Safari Extensions. The convenience of browser extensions has driven their ubiquitous adoption—recent research indicates that 99 percent of employees within surveyed organizations have at least one browser extension installed, with 52 percent maintaining more than ten extensions. This near-universal adoption reflects how extensions have woven themselves into the daily fabric of work and personal computing.
However, this ubiquity masks a fundamental security paradox. While extensions can provide substantial utility through ad blocking, password management, security tools, and productivity enhancements, they simultaneously represent a significant attack surface that threat actors continue to exploit. The integration of extensions directly into browser applications means they do not generate process start events that traditional security tools monitor, allowing malicious extensions to hide in plain sight, carrying out harmful activities without detection for significant periods. This detection gap, combined with the extensive permissions extensions require to function, creates an ideal environment for malicious actors to operate.
The Threat Actors’ Perspective
Understanding why browser extensions have become such attractive targets for threat actors provides essential context for evaluating security risks. Browser extensions offer attackers multiple advantages that make them preferable to traditional malware vectors. First, extensions can access an enormous volume of sensitive data including saved credentials, session cookies, browsing history, clipboard contents, and the ability to monitor all web traffic. Second, extensions already enjoy a baseline of user trust, particularly when installed from official marketplaces, which significantly reduces user skepticism about their activities. Third, the automatic update mechanism built into all major browsers allows attackers to push malicious payloads to millions of users simultaneously without requiring any user interaction or awareness. Fourth, extensions operate within the browser’s trusted context, allowing them to intercept web requests, inject content into pages, and perform actions on behalf of the user across multiple websites and applications.
From a monetization perspective, malicious extensions can generate revenue through multiple mechanisms including ad injection, affiliate link stuffing, credential harvesting for account takeover and identity fraud, and selling harvested data to third parties or cybercriminal groups. The business model is sufficiently lucrative that organized crime groups and nation-state actors have both been observed leveraging browser extensions as attack vectors. The Kiron malware family exemplifies this sophistication, as attackers weaponized browser extensions in 2024 to exfiltrate sensitive user data such as email addresses and browser cookies, with the extensions embedded as encrypted ZIP files within the malware’s core that included scripts to scan webpages for email addresses and monitor webmail tabs to steal cookies.
The Anatomy of Browser Extension Security Risks
Permissions Overreach and Excessive Access
The foundation of browser extension security risks stems from the permission model that governs what extensions can access and modify. When users install an extension, they are typically presented with a list of permissions the extension requires, framed as functional necessities. However, the principle of least privilege—the security concept that software should have only the minimum permissions necessary to perform its intended function—is frequently violated by both legitimate and malicious extensions. Over half of extensions reviewed in production environments required what could be considered excessive permissions, with these elevated permissions posing serious risks that potentially enable malicious actors to monitor web traffic or alter browser tabs.
The most dangerous permission categories include “read and change all your data on all websites,” which grants access to every page visited and everything entered on those pages; “access your browsing history,” which creates a complete record of user web activity; and “manage your downloads,” which can be used to redirect downloads or modify downloaded files. Medium-risk permissions include accessing data on specific websites and managing browser tabs, while lower-risk permissions include reading bookmarks or browsing history. The challenge for users evaluating extensions lies in the fact that many legitimate extensions do genuinely require broad permissions to function properly. A password manager must access all websites to autofill credentials, an ad blocker must see all page content to identify and block ads, and a privacy tool must monitor all web traffic to prevent tracking.
This tension between functionality and security creates a fundamental problem: users cannot simply reject all extensions requesting broad permissions without eliminating access to tools they have come to depend on. Instead, effective vetting requires understanding why an extension requires specific permissions and whether those requirements make sense for the extension’s stated purpose. An extension claiming to add functionality to YouTube but requesting permission to access all data on all websites should be rejected immediately, as the functionality described does not necessitate such broad access. Conversely, an ad blocker requesting “read and change all your data on all websites” may be making a legitimate request, though even then, users should verify that the extension only functions when explicitly enabled rather than operating in the background by default.
Data Exfiltration and Privacy Violations
Beyond excessive permissions, malicious extensions can conduct data exfiltration through multiple mechanisms. The most straightforward approach involves harvesting credentials and session tokens that grant access to user accounts across multiple services. When an extension gains access to cookies—the small data files websites use to maintain user sessions—it can potentially hijack those sessions without ever obtaining the user’s password. This technique, known as session hijacking or cookie theft, allows attackers to impersonate users on banking websites, email services, social media platforms, and any other authenticated service the user was previously logged into. An attacker controlling hijacked sessions can drain bank accounts, access private messages, post content on behalf of the user, and commit identity fraud on a substantial scale.
The sophistication of modern extension-based data theft extends beyond simple credential harvesting. Extensions can monitor keystrokes to capture passwords and sensitive information as users type them, monitor web requests to capture data submitted through forms, access clipboard data to monitor everything the user copies or pastes, and even access webcam and microphone data if permissions are granted. The data harvesting can be selective and targeted, focusing on high-value targets. For instance, the Cyberhaven extension compromise of December 2024 specifically targeted Facebook Ads accounts, suggesting the attackers had identified a lucrative value from that particular access point. Similarly, the RedDirection campaign, which affected at least 36 malicious extensions exposing over 16.3 million users, primarily focused on hijacking browser sessions to targeted social media and financial platforms.
The challenge in detecting such data exfiltration stems from the fact that extensions can communicate with external servers through standard web requests that appear indistinguishable from legitimate traffic. Without deep packet inspection or behavioral anomaly detection, an extension quietly sending stolen data to an attacker-controlled server appears to any network monitoring tool as normal browser traffic. This is precisely why having a solution in place that blocks communication to threat actor infrastructure will effectively neutralize these malicious extensions, and if they are unable to ‘call home,’ the extensions cannot fulfill their intended goal, preventing any damage they would have otherwise caused.
Malware Distribution and Payload Injection
Browser extensions can serve as distribution vectors for additional malware beyond the extension code itself. Extensions can download and execute additional code from remote servers after installation, a technique known as staged malware delivery. This approach allows attackers to circumvent security review processes by initially distributing a seemingly benign extension that only downloads malicious payloads after passing security reviews and building a user base. The PDF Toolbox extension exemplified this technique, downloading additional payloads upon installation to enhance its capabilities and persistence.
Content injection represents another critical risk category. Malicious extensions can inject JavaScript into every webpage a user visits, allowing them to modify page content, redirect users to phishing sites, create fake login forms overlaid on legitimate sites, or inject advertisements. Social engineering through fake content injection can be particularly effective, as users trust the websites they believe they are visiting and may not immediately recognize injected content as fraudulent. An extension that injects a fake login form onto a banking website or redirects a user attempting to access their email to a phishing replica can harvest credentials from millions of users. The RedDirection campaign exemplified this technique, with extensions capable of issuing real-time redirects to phishing or malware-laden pages, with scenarios including redirecting users attempting to join Zoom meetings to fake update pages or spoofing banking logins to harvest credentials.
Extensions can also manipulate web requests in real time through the webRequest API or the newer declarativeNetRequest API. These APIs allow extensions to intercept network requests before they reach the server, modify them in transit, and modify responses before the browser processes them. A malicious extension could redirect financial transactions, modify cryptocurrency addresses in copy-paste operations, or alter transaction details on banking websites to mislead users. The power of these APIs is such that using capabilities allowed within permissions such as declarativeNetRequest, threat actors could target a brand like an Office 365 login portal and redirect it to a phishing portal, all under the same permission that was already approved for use.
The Threat Landscape: Recent Major Incidents and Patterns
The February 2025 GitLab Intelligence Discovery
A particularly instructive recent incident emerged in February 2025 when the GitLab Threat Intelligence team identified a significant security breach affecting legitimate extensions. The investigation uncovered at least 16 malicious Chrome extensions affecting over 3.2 million users, with these extensions previously operating as legitimate tools installed through official browser stores from trusted developers. What made this incident particularly notable was that the extensions were corrupted through malicious updates rather than being intrinsically malicious from inception. The investigation determined that this attack originated from compromised developer accounts, with some developers having stopped supporting their extensions and lost control over them, while others were likely deceived through phishing kits targeting extension developers specifically.
This incident illustrates a critical vulnerability in the extension ecosystem: legitimate developers represent attractive targets for attackers because they already have user bases and established trust. Once attackers gain control through phishing or account compromise, they can push updates that introduce hidden scripts capable of covertly stealing data, modifying web requests, and injecting advertisements. Notably, these malicious changes largely went unnoticed by users, as they had already granted the necessary permissions, allowing attackers to manipulate web content and user interactions seamlessly. The extensions affected included popular categories such as ad blockers (Adblocker for Chrome — NoAds, Adblock for You, and Adblock for Chrome), color pickers, emoji keyboards, and weather tools. The permissions these extensions had already been granted—such as “host access” and “scripting controls”—posed significant risks, as they enabled the extraction of sensitive information including credit card details, login credentials, authentication tokens, and cookies.
The RedDirection Campaign and Verified Badge Compromise
An even larger scale incident emerged with the RedDirection campaign, in which researchers uncovered 36 malicious Chrome and Edge extensions in the campaign, exposing 16.3 million users. This campaign demonstrated a sophisticated understanding of how to exploit user trust through the marketplace verification system. The extensions involved in RedDirection bore Google’s prestigious “verified” badge and featured placements, covertly compromising over 1.7 million users with a subset of analysis. These extensions maintained legitimate functionality while secretly conducting malicious activities—for instance, the Color Picker extension “Color Picker, Eyedropper Geco colorpick” continued to function as a legitimate tool while simultaneously hijacking browser sessions, tracking every website visited, and establishing persistent backdoors through command and control infrastructure.
The RedDirection campaign is particularly significant because it demonstrates how verification badges and marketplace featured placements can be weaponized against users. Extensions like “Video Speed Controller,” “Volume Max,” “Unlock Discord – VPN Proxy,” and “Free Weather Forecast” all maintained their promised functionality while secretly surveilling user activity on every tab navigation. The malicious code tracked browsing activity, sending unique identifiers and URLs to remote servers, and could issue real-time redirects to phishing or malware-laden pages. The deployment method was particularly insidious: the malware was deployed through version updates, meaning millions of users who trusted these extensions experienced seamless, automatic infection without ever needing to interact with the extension post-install.
The Cyberhaven Developer Compromise
The Cyberhaven incident in December 2024 provides an instructive case study in sophisticated supply chain attacks targeting extension developers themselves. On December 24, 2024, a phishing attack compromised a Cyberhaven employee’s access to the Google Chrome Web Store, with the attacker then uploading a malicious version of Cyberhaven’s Chrome extension (version 24.10.4). What made this attack particularly noteworthy was how the attacker overcame multiple security layers. The attacker sent a phishing email to Cyberhaven’s publicly listed support email claiming to be from the Chrome Web Store and alleging policy violations. When the employee clicked the link, they were redirected to a legitimate Google authorization flow for a malicious OAuth application named “Privacy Policy Extension.” Despite the fact that the employee had multi-factor authentication (MFA) and Google Advanced Protection enabled, the attacker successfully gained access.
This incident reveals that even well-resourced companies with security-conscious employees and advanced protective measures can fall victim to sophisticated social engineering attacks. The attacker’s success in bypassing MFA and Advanced Protection indicates the use of advanced phishing techniques, possibly including credential harvesting or account takeover. Once the attacker gained Chrome Web Store access, they uploaded a modified version of the legitimate Cyberhaven extension with additional code to reach out to command and control servers and collect data from hardcoded websites. Notably, the malicious extension passed the Chrome Web Store’s security review, highlighting critical gaps in Google’s review processes.
Broader Patterns in Extension Compromise
These incidents are not isolated occurrences but rather exemplars of broader patterns in the extension ecosystem. Research indicates that in January 2025 alone, at least 33 compromised Chrome browser extensions were identified, with reports suggesting over 2.6 million users were impacted, and the compromised extensions were used for up to 18 months. This extended operational period before discovery indicates that automated detection systems and user reporting mechanisms are insufficient to identify compromised extensions in real time.
The common thread across these incidents is that attackers recognize extension marketplaces as high-value targets offering access to millions of users with minimal friction. Once attackers establish control over an extension—whether through developer account compromise, extension purchase, or exploitation of security vulnerabilities—they can distribute malicious updates through the automatic update mechanism to the entire user base. From the attacker’s perspective, this represents an extraordinarily efficient attack vector: millions of users automatically receive malicious code without being prompted to grant new permissions, as the update mechanism operates silently in the background.
Marketplace Vulnerabilities and the Systemic Review Gap
The Chrome Web Store Review Process and Its Limitations
The Chrome Web Store, which hosts over 140,000 extensions, relies on both automated and manual review processes to identify malicious submissions before they reach users. However, this review process faces significant scalability challenges and has demonstrated critical gaps in enforcement. In 2024, less than one percent of all installs from the Chrome Web Store were found to include malware, a statistic Google presents as evidence of effective review processes. However, this seemingly positive statistic obscures the reality that 1 percent of billions of installations still represents a massive number of compromised users, particularly when considering that a single compromised popular extension can affect millions.
The review process specifically targets certain signals that increase review time and scrutiny, including submissions from new developers, new extensions, dangerous permission requests, and significant code changes. However, the practical reality is that reviews may take considerably longer for extensions requesting broad host permissions or sensitive execution permissions, or which include a lot of code or hard-to-review code, with the review process flagging patterns like `*://*/*`, `https://*/*`, and `` that grant extensions extensive access to user web activity. Despite these review signals, many problematic extensions still achieve approval, and the review of updated versions of already-published extensions is fundamentally different from the review of new submissions.
Enforcement Gaps and Systematic Issues
The most concerning aspect of the extension marketplace security landscape involves the lax enforcement of policies against spam, malicious updates, and policy violations. One security researcher documented over 920 extensions using tricks to spam the Chrome Web Store, with most belonging to a few large extension clusters. Despite reporting these extensions, Google’s response has been characterized as entirely reactive, typically limited to extensions that have already caused considerable damage. The researcher noted that Google appears to have been made aware of particular spamming tricks a year before their blog post but chose not to act on this information. This reactive rather than proactive posture suggests that marketplace maintenance is not a priority for Google, despite Chrome’s market dominance eliminating competitive pressure to maintain marketplace quality.
The practical consequence of this lax enforcement is that the Chrome Web Store has become a venue where malicious actors can operate with relative impunity. The same security researcher documented how 96 extensions from a malicious cluster of 108 identified extensions remained active in January 2025, despite having been reported. Extensions in this cluster engaged in aggressive monetization schemes including ad injection into Google search results through sophisticated steganographic techniques, cookie stuffing for affiliate fraud, and deployment as time bombs that could activate malicious functionality at any point in time. These extensions manipulated Google’s search results page by invisibly injecting custom elements that redirected clicks to monetized pages, essentially stealing clicks from legitimate search results.
Developer Account Vulnerability and Acquisition
A systemic vulnerability that emerges from marketplace incidents involves the ease with which developer accounts can be compromised or extensions can be purchased. Security research demonstrated that an extension named “Website Blocker” was purchased for $50 and transferred ownership to a new account for a $5 Chrome Web Store fee. Once control was transferred, the owner submitted an update to the Chrome Web Store that was approved and pushed to all users. This research showed that it is “absolutely impossible” for browser extension users to know when ownership changes hands or extensions they use are repurposed for potentially malicious intent. The researcher used the existing “declarativeNetRequest” API permission that was already approved for the extension to redirect traffic from a specific URL to a “Rickroll,” demonstrating that even the relatively limited modification to an already-approved extension receives minimal scrutiny.
This purchasing mechanism has become a known attack vector. Attackers specifically seek out extensions that are no longer actively maintained by their original developers, recognizing that such extensions can be purchased cheaply and then updated with malicious code. The large existing user bases of such extensions mean that malicious updates will be automatically pushed to millions of users who trust the tool and have already granted broad permissions. The fundamental problem is that browser extension updates, by default, occur automatically and silently when a user’s browser detects a new version available in the Chrome Web Store, with only new permission requests triggering user notification or prompts.
Pre-Installation Vetting Methodologies
Developer and Source Verification
Effective vetting before installing an extension begins with understanding the developer and verifying the legitimacy of the source. Users should verify the developer’s legitimacy by looking for a professional developer with a public profile or website, and if the website doesn’t have an HTTPS connection or if other suspicious elements like a vague privacy policy are observed, it is best to avoid installing that extension. This initial verification step weeds out obviously fraudulent actors but should not be considered sufficient, particularly given that legitimate developers have also been successfully compromised through phishing attacks.
Checking the developer’s history provides additional context. If a developer has published multiple extensions over time, this suggests legitimate development activity and provides more surface area for security researchers to analyze. Conversely, a developer publishing a single extension through a generic Gmail address with no other online presence represents a significantly higher risk profile. Recent research indicates that 54 percent of extension publishers lack a verifiable identity beyond a generic Gmail address, and 79 percent of all publishers have released only a single extension. This fragmentation makes it extremely difficult for IT teams or individual users to conduct meaningful reputation checks.
One specific indicator of developer legitimacy involves the presence of verified badges or official designation in the marketplace. For Chrome, a “verified” badge indicates that Google has verified the developer’s identity. For Firefox, a “recommended” label serves a similar function. However, as the RedDirection campaign demonstrated, these badges can provide false assurance, particularly when extensions have been compromised after initial publication. The presence of a verified badge or recommended status should be viewed as a positive signal rather than a definitive guarantee of safety.
Permission Analysis and Risk Assessment
Upon identifying a candidate extension, users must conduct a detailed review of the permissions the extension requests. The first step involves understanding what permission categories exist and their associated risk levels. Google’s framework identifies high alert permissions that access all data on the computer and websites visited, medium alert permissions that access data on all visited websites, and low alert permissions that access bookmarks, browsing history, or installed extensions. This framework provides a starting point, but users must go further to understand whether the requested permissions align with the extension’s stated purpose and functionality.
A practical methodology involves asking specific questions about each requested permission. For an ad blocker, the question is whether it needs to read and modify all website content to function. The answer is generally yes, as ad blockers must examine every element on every page to identify ads. However, an ad blocker should not need access to browsing history, downloads, or personal files outside the browser. If an ad blocker requests such permissions, the extension should be rejected. For a password manager, the extension must access all websites to identify login fields and autofill credentials, so broad permissions are justified. However, a password manager should encrypt data locally and never transmit unencrypted credentials to external servers, so users should investigate the extension’s privacy practices to verify this claim.
The most informative resources for permission analysis include CRXcavator, a Chrome Extension security assessment automation tool designed to help security analysts have better insight into Chrome extensions. CRXcavator scans extensions in the Chrome Web Store and assigns risk scores based on factors including permissions, code patterns, and network communications. Users can search for specific extensions on CRXcavator and review the detailed risk assessment report. Extensions with risk scores above 500 or critical permission risks should not be installed. The tool provides transparent reporting on what permissions the extension requests, what API calls it makes, and any suspicious patterns detected in the code.
Download Volume and User Reviews
The popularity and user reception of an extension provides useful signals about its safety, though these signals can be manipulated. An extension that has many downloads is generally (but not always!) safer, because there is a greater chance that existing users would have already detected bad behavior. High-volume extensions have been scrutinized by more security researchers, are more likely to be analyzed in academic research, and have larger user bases that report issues. However, as the RedDirection campaign demonstrated, extremely popular extensions with hundreds of thousands or millions of installs can still be compromised.
User reviews provide direct feedback about whether an extension behaves as advertised. Users often report unexpected behavior in reviews, allowing potential installers to identify extensions that do not match their advertised functionality. For instance, users who discovered that extensions were injecting advertisements, stealing data, or redirecting traffic often reported these behaviors in review comments. Negative reviews mentioning strange ads placement, affiliate IDs appearing in service links, or suspicious browser behavior should raise concerns. However, reviews can be faked, and sophisticated attackers may suppress negative reviews or flood review sections with positive fake reviews.
The extension store rating provides another data point. Extensions with ratings below 4 out of 5 stars warrant careful investigation into what problems users are reporting. However, extensions with very high ratings should also be scrutinized, as early versions of compromised extensions may have maintained high ratings before malicious updates were pushed. The temporal pattern of reviews can be revealing—if recent reviews are significantly more negative than older reviews, the extension may have been recently compromised.
Privacy Policy and Data Handling Practices
The privacy policy represents a critical but often overlooked component of extension vetting. Browsers require developers to disclose what data their extensions collect and how they handle that data. Users should review the privacy policy to understand data usage, and should be cautious when the privacy policy is vague, buried on an external website, or contradicts the extension’s stated functionality. Firefox specifically requires that the privacy policy be included in full within the extension listing rather than requiring users to navigate to an external website.
Key questions about privacy policies include whether the extension collects browsing history, and if so, what it does with that data; whether the extension collects and transmits personally identifiable information; whether the extension uses cookies or similar tracking technologies; and whether the extension shares data with third parties. Extensions that claim to block tracking or protect privacy should have explicit privacy policies disclosing what they do not collect. Conversely, an extension that collects browsing data should clearly explain why it needs this data and how it securely stores and transmits it.
One particularly problematic pattern involves privacy policies that contradict extension marketplaces’ representations of the extension’s data practices. For instance, the Karma extension claimed in the Chrome Web Store that “This developer declares that your data is not being sold to third parties, outside of the approved use cases,” but this statement was contradicted by their privacy policy, which disclosed that they collected and sold browsing data. This contradiction indicates deception about the extension’s actual data practices.
Technical and Behavioral Analysis Tools
Automated Security Assessment Platforms
Beyond manual review, several platforms provide automated security assessment of browser extensions. CRXcavator is a Chrome Extension security assessment automation tool designed to help security analysts have better insight into Chrome extensions, providing security and risk context around Chrome plugins and enabling analysts to know if any plugins running pose associated risks. The tool has been widely adopted by security teams for evaluating extensions before approving them for use. Similar tools include Spin.AI, which uses artificial intelligence to assess browser extension risks and provide risk scores and levels, and enterprise solutions from vendors like LayerX and Seraphic that provide comprehensive browser extension discovery, monitoring, and risk scoring at scale.
These platforms analyze extensions across multiple dimensions including requested permissions, API usage patterns, network communications, code obfuscation, and known vulnerability databases. They generate risk scores that aggregate these factors into a single metric that helps users quickly identify high-risk extensions. The advantage of automated tools is that they can analyze extensions rapidly at scale and identify patterns that might not be immediately obvious to manual review. The limitation is that these tools can only analyze static properties of the extension and cannot always predict how extensions will behave in runtime situations or after receiving updates.
Manual Code Review and Analysis
For extensions that will be deployed in high-security environments or that handle sensitive data, manual code review of the extension source code provides the most thorough analysis. Extensions can be decompiled and their source code examined using JavaScript deobfuscators and analysis tools. Users should look for suspicious API calls including `chrome.tabs` to capture screenshots or tab data, `chrome.cookies` to access authentication data, `chrome.storage` to access stored sensitive information, and network calls to external domains. The presence of encoded or obfuscated code should be treated as a red flag, as malicious extensions frequently obfuscate their code to evade detection.
Legitimate extensions may use code minification for performance optimization, but developers should be prepared to provide source maps or non-minified code upon request for security review. Extensions that cannot or will not provide clear, non-obfuscated source code for inspection should not be trusted with sensitive operations. Conversely, open-source extensions that publish their source code on platforms like GitHub provide transparency that users can verify and that security researchers can audit.
Permission Monitoring and Behavioral Analysis
For extensions that have already been installed, ongoing monitoring of extension permissions and behavioral patterns provides a second layer of detection. Enterprise tools can monitor which extensions access sensitive data categories including cookies, saved passwords, browsing history, and page contents, identifying when extensions use permissions in unexpected ways. For instance, an extension that claims to only modify page styling but requests and uses clipboard access would represent suspicious behavior warranting investigation.
Browser vendors have begun implementing safety checking features to identify potentially harmful extensions. Chrome’s Safety Check feature, for instance, warns users of any installed extensions that might pose a security risk, and allows users to remove potentially unsafe extensions with a single click. However, these built-in safety features have limitations—they rely on Google’s own analysis and cannot identify 0-day vulnerabilities or newly compromised extensions before Google’s systems detect the compromise.
Best Practices for Extension Vetting and Installation
Individual User Best Practices
For individual users, effective extension security begins with minimizing the number of extensions installed. Every installed extension increases the potential for compromise, making a minimalist approach essential for security. Users should keep only those extensions that are critical to their tasks, recognizing that many extensions offering similar functionality exist, and if one tool does not meet security and privacy preferences, it may be possible to find a reputable alternative offering the same features with added security. Rather than accumulating dozens of extensions over years without reassessment, users should conduct regular audits—ideally quarterly—of all installed extensions, removing any that are no longer actively used.
When installing an extension, users should follow a structured vetting process before granting installation permission. The process should include checking the developer’s website to verify legitimacy, reading the extension description carefully for red flags including unexpected data sharing or tracking, reviewing user comments and ratings for complaints about unexpected behavior, checking if the extension is actively maintained with recent updates, verifying that requested permissions align with the extension’s stated function, and if any doubt remains, consulting online resources like CRXcavator or security forums.
After installation, users should monitor extension behavior for unexpected changes. Updates to permissions, changes in functionality, or unexpected network communications should trigger removal of the extension. Users should enable automatic updates for extensions they choose to keep, but should not treat automatic updates as a guarantee of safety, as demonstrated by multiple cases of compromised extensions pushing malicious updates. Users should periodically review their installed extensions through the browser’s extension management interface, removing any extensions they no longer actively use and disabling any extensions that are not needed for their current browsing session.
Enterprise and Organizational Best Practices
For organizations, browser extension security requires a more structured approach involving discovery, risk assessment, policy development, and ongoing monitoring. Organizations should begin by creating a comprehensive inventory of all browser extensions installed across their user base, leveraging browser management APIs and endpoint management solutions to enumerate every extension including both official store installs and sideloaded add-ons. This unified dataset serves as the single source of truth for subsequent risk assessments and policy enforcement.
With an inventory in hand, organizations should classify extensions according to their primary function and inherent risk profile, mapping each category to a preliminary risk tier. Productivity tools, security tools, AI assistants, media management tools, and other categories warrant different risk assessments. GenAI tools and data-scraping extensions inherently require broader permissions and warrant higher scrutiny, while UI-only extensions such as dark-mode toggles may pose minimal threat if they limit themselves to presentation logic. This categorization helps IT leaders prioritize oversight and allocate resources effectively.
Organizations should then assess the permissions declared by each extension, focusing on the most sensitive flags including “read and change all data on websites you visit,” “access your browsing history,” and “manage downloads,” while not overlooking less obvious permissions like “nativeMessaging” or “cookies”. A permission-centric risk matrix correlating specific scopes with potential impact enables identification of particularly dangerous permission combinations, such as “cookies” plus “history” access enabling session hijacking, or “webRequest” permissions enabling request manipulation and injection of malicious payloads.
The risk assessment should incorporate technical permissions, publisher reputation, update frequency, user adoption rates, and marketplace ratings into a composite risk score. Extensions from unknown publishers with outdated versions requesting high-impact permissions and installed on significant fractions of endpoints should trigger high-risk alerts. Modern security platforms can automate this scoring, generating dynamic dashboards that surface emergent threats in real time. Armed with nuanced risk profiles, organizations can implement adaptive policies beyond simple allowlists or denylists, applying policies tailored to user roles, departments, or sensitivity levels.
Chrome Web Store and Firefox Standards
For Chrome environments specifically, Google’s Chrome Web Store provides extension management capabilities that organizations can leverage. Google provides policy controls allowing organizations to manage extensions through the Google Admin console, Windows Registry, and Windows Group Policies. Organizations can block extensions based on permissions they request, force install specific approved extensions, or maintain an on-premises web store of pre-approved extensions. However, these controls require active management and understanding of organizational security policies.
Firefox has implemented slightly more stringent requirements for extension developers compared to Chrome. Firefox’s data minimization policy requires that extensions only collect data necessary for their functionality, and explicitly prohibits collection of search terms and browsing history unless necessary for the extension’s primary function. Firefox also requires clear disclosure of data collection practices within the extension itself, not just on external websites, providing users more direct access to privacy information. Additionally, Firefox requires that users provide affirmative consent for data collection, not merely notice.
Concluding Your Security Vet
Browser extension security represents one of the most significant yet underappreciated security challenges in contemporary digital environments. The evolution from the RedDirection campaign affecting 16.3 million users to the broader ecosystem of compromised legitimate extensions demonstrates that threat actors have developed sophisticated techniques for infiltrating extension marketplaces and leveraging them to compromise millions of users. The fundamental tension between the functionality extensions provide and the security risks they introduce cannot be eliminated—extensions by their nature require broad permissions to function effectively, and those permissions create opportunities for abuse.
Effective browser extension security requires vigilance from multiple actors. Browser vendors must strengthen their review processes to catch both intrinsically malicious extensions and legitimate extensions that are subsequently compromised. The existing reactive approach must shift toward proactive identification and remediation of compromised extensions, with faster response mechanisms when security incidents occur. Developers must prioritize security in their extension design, implement the principle of least privilege by requesting only necessary permissions, and establish secure development practices preventing account compromise through phishing and other social engineering techniques.
For users—whether individuals or members of organizations—extension security requires understanding that each installed extension represents a calculated risk-benefit tradeoff. The practical reality is that browser extensions have become essential for modern web usage, with ad blockers, password managers, and productivity tools providing substantial value. However, this reliance should not lead to complacency. Before installing any extension, users should conduct structured vetting examining the developer’s legitimacy, the permissions requested, the extension’s functionality, user reviews, privacy practices, and risk scoring from tools like CRXcavator. Users should minimize the extensions they install to those truly necessary for their workflow, maintain awareness of what their extensions can access and do, periodically audit their installed extensions, and quickly remove extensions that exhibit suspicious behavior or are no longer actively used.
Organizations must treat browser extension security as a critical component of their broader cybersecurity strategy, recognizing that extensions represent a significant attack surface that traditional endpoint security tools often fail to monitor effectively. Enterprise extension security requires automated discovery of all installed extensions, systematic risk assessment incorporating multiple data sources, policy-based management with different rules for different user populations, and continuous behavioral monitoring for suspicious extension activity. The investment in these capabilities—whether through developing internal solutions, leveraging browser vendor management capabilities, or implementing specialized security platforms—represents a necessary cost of operating in environments where browser extensions have become ubiquitous.
The browser extension ecosystem will likely continue evolving as threats sophisticate and security controls improve. Manifest V3’s shift away from certain extension capabilities in Chrome aims to reduce certain attack vectors, though early evidence suggests determined threat actors continue finding workarounds. Marketplace vendors may eventually implement more sophisticated real-time monitoring of extension behavior rather than relying primarily on code review at publication time. Users and organizations may increasingly demand that extension developers implement transparent logging of extension activities, supporting user and security team auditing of extension behavior in real time.
Until these improvements materialize, the responsibility for ensuring extension security rests primarily with users and organizations. By understanding the threat landscape, implementing structured vetting processes before installation, maintaining awareness of extension behavior post-installation, and rapidly removing extensions that exhibit suspicious activity, users can substantially reduce the risk that browser extensions pose to their security and privacy. The goal is not to eliminate browser extensions entirely—the functionality they provide is too valuable to dismiss—but rather to approach them with appropriate skepticism and implement the technical and procedural controls necessary to mitigate the genuine risks they represent.
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