Malicious browser extensions expose a browser identity gap

At a glance

What this is: This is a practitioner guide on malicious browser extension governance, and its key finding is that trusted extensions can turn malicious after approval or purchase.

Why it matters: It matters because browser extensions sit between human identity, session state, and enterprise secrets, so IAM and security teams need control points that see installation, ownership change, and risky update behaviour.

By the numbers:

• The Chrome extension store alone has in excess of 100k extensions with a wide range of use cases.

👉 Read Push Security's guide to managing malicious browser extensions

Context

Browser extensions now function as a practical identity and access layer inside the employee browser, not just as convenience add-ons. That matters because an extension can inherit session context, inspect content, and interact with web applications without triggering the same controls that govern traditional software installs or privileged access.

The governance problem is that approval at install time does not guarantee safety later. A legitimate extension can be bought, phished, or updated into a malicious state after it is already trusted, which leaves the security team trying to govern change rather than just initial admission.

Key questions

Q: What breaks when malicious browser extensions are not governed properly?

A: What breaks is the assumption that browser trust is fixed at install time. A legitimate extension can be updated, repurchased, or repurposed into a malicious payload after approval, which means browser secrets, sessions, and web app actions can all be exposed without a new software deployment event.

Q: Why do browser extensions increase identity and access risk?

A: Browser extensions sit inside the authenticated browser session, so they can observe or influence access without a separate login. That makes them risky in environments where users rely on browser-stored credentials, synced profiles, and web applications that carry sensitive session state.

Q: How do security teams decide which browser extensions to allow?

A: Start with a live inventory, then review install count, publisher trust, ownership history, permissions, deployment method, and whether the extension has been unlisted or recently updated. Allow only what is needed for business use, and remove anything that creates more exposure than value.

Q: What should teams do when extension syncing crosses work and personal profiles?

A: Treat synced browser profiles as a boundary issue, not a convenience setting. If a personal profile can sync extensions into a work browser, separate the profiles, reduce syncing where possible, and review whether browser access is being inherited across devices that do not share the same security posture.

Technical breakdown

Why browser extensions become a hidden identity control surface

Browser extensions often operate with access to tabs, pages, credentials, and application content that users already trust. That makes them an identity-adjacent control surface because they can observe or manipulate authenticated sessions without needing separate credentials. The threat is not only installation, but post-install change, ownership transfer, and update drift. Static store review helps, but it cannot reliably determine whether a once-benign extension will later switch behaviour through a malicious update or obfuscated payload.

Practical implication: treat extensions as governed runtime software, not one-time approvals.

Allowlisting and blocklisting as browser identity controls

Allowlisting reduces exposure by limiting the set of extensions permitted to run, while blocklisting removes known-bad items as they are identified. In practice, the security value comes from coupling policy with visibility, because a list alone cannot answer whether an extension is already installed, enabled, sideloaded, or updated by an untrusted publisher. A workable model also needs request handling for legitimate business exceptions, otherwise users will route around controls through unmanaged browsers or personal profiles.

Practical implication: pair allowlists with request workflows and enforcement across managed browsers.

Why extension syncing changes the risk model

Browser syncing can extend a single extension decision across multiple devices and profiles, which turns one compromise into a broader trust problem. If a personal profile is signed into a work browser, extension state can travel with it, along with the risk that a less secure personal device becomes the source of enterprise exposure. That means browser governance has to consider profile separation, sync settings, and the trust boundary between work and personal identity contexts.

Practical implication: disable or constrain browser sync where extension governance is not yet mature.

Threat narrative

Attacker objective: The attacker aims to turn a trusted browser extension into a scaled browser compromise that exposes browser secrets and session-controlled enterprise access.

1. Entry begins when an attacker compromises a legitimate extension path by phoning a developer account, purchasing an existing extension, or inserting malicious code into an update channel.
2. Credential access or abuse occurs when the malicious extension gains browser-level visibility into sessions, pages, and browser-stored secrets after users install or update it.
3. Impact follows when the compromised extension runs across many employee browsers and can steal browser secrets, interact with web applications, or widen access through synced profiles.

Breaches seen in the wild

• Cisco DevHub NHI breach — IntelBroker exploited exposed Cisco credentials, API tokens and keys in DevHub.
• ASP.NET machine keys RCE attack — 3,000+ exposed ASP.NET machine keys enabled remote code execution.

Read our 52 NHI Breaches Analysis report for a comprehensive view of breaches impacting Non-Human Identities including AI Agents.

NHI Mgmt Group analysis

Browser extension governance is an identity problem, not just a software inventory problem. Extensions operate inside authenticated sessions and can act on behalf of the user without receiving separate identity events. That means the control plane has to see more than install state, because ownership change, update drift, and browser sync can all alter risk after approval. Practitioner conclusion: extension governance belongs in the same conversation as session security and browser-based access control.

Store approval is a weak proxy for runtime trust. The article shows why static checks and manual review cannot be the sole trust model when attackers can wait, update, or smuggle code after publication. This is a browser identity failure mode because the trusted object changes after the trust decision is made. Practitioner conclusion: governance must follow extension lifecycle, not just procurement or initial allowlisting.

Identity blast radius expands when one extension decision propagates across browsers. A single malicious update can affect many users, and browser syncing can carry risk from a personal profile into a work context. This is the same structural problem that appears in other non-human identity domains: one trusted object can become a multiplier for exposure. Practitioner conclusion: reduce the number of extensions that can multiply across the workforce.

Ephemeral browser trust debt: Extension risk accumulates when organisations defer pruning, ownership review, and update monitoring after initial approval. The extension is treated as stable even though its publisher, permissions, and code path can change. Practitioner conclusion: teams need to govern the full extension lifecycle as a living trust object, not a static approved asset.

From our research:

• The average organisation believes more than 1 in 5 of their non-human identities are insufficiently secured, according to the 2024 ESG Report: Managing Non-Human Identities.
• Two-thirds of enterprises have endured a successful cyberattack resulting from compromised non-human identities, with a quarter encountering multiple attacks.
• Browser extensions are a different control problem from workload identity, but the governance pattern is the same, as explained in the NHI Lifecycle Management Guide.

What this signals

Identity blast radius: browser extension risk now behaves like a lifecycle problem, because one trusted add-on can change state after approval and propagate across many users. Security teams should expect extension governance to merge with browser posture, access review, and session protection rather than remain a separate admin task.

The category gap is widening as extension ecosystems grow and attackers use update channels, ownership changes, and browser sync to extend reach. For practitioners, the practical question is no longer whether extensions exist in the estate, but which ones can change behaviour after trust has already been granted.

For practitioners

• Inventory every extension in use Build a live list of extension name, ID, version, permissions, deployment method, and which employees and browsers have it installed. Use that inventory to separate managed, sideloaded, and development extensions before you decide what to allow.
• Block known-bad extensions by default Configure enforcement so reported malicious extensions are disabled rather than merely observed, and make sure the control also blocks store access where possible. That reduces the chance that a malicious update can execute before triage completes.
• Prune the allowlist continuously Review ownership changes, install counts, and permission changes on a regular cadence so previously acceptable extensions do not remain trusted after their risk profile shifts. Remove anything that is no longer needed for a real business function.
• Separate work and personal browser profiles Where browser sync is still enabled, confirm that work browsing is not tied to a personal profile and that synced extensions cannot bridge those identities. This is especially important when users sign into work browsers with consumer accounts.

Key takeaways

• Browser extensions are now part of the identity trust boundary because they operate inside active sessions and can inherit browser access.
• A legitimate extension can become malicious after approval, so store review alone is not a sufficient control model.
• Continuous inventory, default blocking of known-bad extensions, and profile separation are the controls that reduce browser-side identity risk.

Key terms

• Browser Extension Governance: Browser extension governance is the set of policies and controls used to decide which extensions may run, how they are reviewed, and when they must be removed. In practice, it covers inventory, approval, monitoring, and lifecycle change management for code that lives inside the browser session.
• Extension Sync Risk: Extension sync risk is the possibility that an extension installed in one browser or profile will propagate to other devices through account synchronisation. It matters because a compromise in one place can spread trust, permissions, and exposure into a separate work context without a new approval event.
• Identity Blast Radius: Identity blast radius is the scope of impact created when a trusted identity object changes behaviour and affects many downstream users or sessions. For browser extensions, a single malicious update can convert one approved tool into a large-scale session compromise across the workforce.

Deepen your knowledge

Browser extension governance and lifecycle control are core topics in our NHI Foundation Level course, the industry's only accredited NHI security programme. If you are building controls for browser-based access risk from the same starting point, it is worth exploring.

This post draws on content published by Push Security: Detect risky and malicious extensions and block them from running in employee browsers. Read the original.