Detecting and Blocking Malicious Browser Extensions with Prisma Browser

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Detecting and Blocking Malicious Browser Extensions with Prisma Browser

By: Tuan Vu  | Almas Raza 

As enterprise work has shifted almost entirely to the browser, browser extensions have emerged as a significant security blind spot. While organizations focus on securing the network perimeter, extensions operate with broad permissions within the browser itself, outside the reach of traditional security controls. This gap has not gone unnoticed by attackers: over 280 million Google Chrome users have installed malicious extensions, underscoring how pervasive and underestimated this threat has become.

While organizations can enforce strict extension allowlists via standard IT policies, the sheer volume and variety of extensions in use make comprehensive oversight difficult. This creates a highly evasive enterprise blind spot: trusted extensions that become weaponized. Because these threats operate directly inside the browser, they effectively bypass traditional network security controls, remaining invisible to firewalls and traditional endpoint protection tools.

 

What Malicious Extensions Can Do

Once installed, these highly evasive extensions possess deep visibility into user sessions and browsing activity. Because they operate with elevated browser permissions, they can silently carry out a wide range of malicious actions without the user or security team ever knowing. Based on observed threat behavior, malicious extensions can execute the following actions:

• Steal Sensitive Data: Silently harvest login credentials, session tokens, authentication cookies, and other sensitive enterprise information, including LLM chat history.
• Hijack Browser Settings & Redirect: Modify local browser configurations and redirect user traffic to attacker-controlled, malicious websites.
• Monitor User Activity: Continuously track browsing behavior, capture keystrokes, intercept form data, and monitor AI conversations.
• Establish C2 Communication: Maintain persistent communication channels with Command and Control (C2) servers to download and deploy additional malware payloads.
• Perform Remote Script Injection: Inject malicious JavaScript into otherwise benign web pages to manipulate content, steal dynamic data, or execute arbitrary code.

 

Real-World Attack Scenarios: How Extensions Are Weaponized

Adversaries use several sophisticated methods to distribute malicious extensions, often exploiting trusted distribution channels and bypassing standard vetting processes. These range from publishing convincing fake extensions on  the Chrome Web Store, impersonating popular tools like DeepSeek or ChatGPT, to long-game campaigns in which threat actors spend years building trust through legitimate extensions before pushing a malicious update to millions of users. In the most targeted cases, attackers compromise legitimate developer accounts through identity phishing and then weaponize extensions that users already trust.

Case Study: The Cyberhaven Incident 

In late 2024, attackers targeted the developers of the Cyberhaven browser extension by tricking a developer into authorizing a malicious OAuth application. This gave the attackers access to publish a compromised version of the extension to the Chrome Web Store. With unauthorized access to the developer's Chrome Web Store account, the attackers uploaded a malicious version of the legitimate extension (version 24.10.4). This poisoned update, containing a worker.js file for C2 communication and a content.js file for data extraction, was pushed to 400,000 users. Because this payload was delivered as an official, signed update through the trusted Chrome Web Store channel, traditional browser trust mechanisms implicitly allowed it, successfully exfiltrating session tokens and targeting SaaS applications.

 

How Does Prisma Browser Identify, Detect, and Block Malicious Extensions?

To combat these highly evasive threats, especially poisoned updates to trusted extensions that evade standard signature checks, Palo Alto Networks built Advanced Extension Security directly into Prisma Browser. Unlike solutions that rely on static blocklists, Advanced Extension Security performs multi-layered analysis to detect both known and unknown malicious extensions.

When an extension is installed or updated, Prisma Browser intercepts it before it can execute and sends it to Palo Alto Networks’ cloud-based services for analysis. A specialized detection engine evaluates the extension across multiple dimensions and delivers a risk score and verdict back to the endpoint in real time.

Our detection architecture delivers these key capabilities:

• Real-time extension analysis powered by an advanced detection engine that inspects extension code, traces how data flows through it, and uses AI to calculate risk, blocking threats before installation.
• Definitive threat classification that goes beyond risk scores, with a confirmed malicious verdict backed by identified malicious behavior, malicious URL infrastructure intelligence and malware insights.
• Continuous monitoring of extensions for threats throughout their update lifecycle.
• Visibility and automated response with risk-based controls, auto-removal of malicious extensions, and end-user notifications.

 

What Action Is Needed to Benefit from Advanced Extension Security?

While traditional group policies require manual, static rules to manage extensions, they offer no visibility into what those extensions are actually doing and no way to detect when a previously trusted extension becomes malicious after an update. To close this blind spot, organizations can elevate their security posture by deploying Prisma Browser, which provides dynamic risk assessment and continuous monitoring that adapts as the threat landscape evolves. 

This provides security teams with comprehensive visibility and dynamic, risk-based control over all extensions operating within the environment, across both managed and unmanaged devices. Administrators can configure policies to automatically block or remove malicious extensions based on real-time threat intelligence rather than static rules.Advanced Extension Security is available today for enterprise deployment in Prisma Browser. 

 

Additional Information

To see Advanced Extension Security in action, schedule a Prisma Browser demo with your Palo Alto Networks team.