Native Messaging Security Risks and Prevention for Browser Extensions

1. Conclusion First: The Risk Is Not the Channel; It Is Boundary Governance

Discussions about communication between browsers and native desktop applications often fall into two extremes. One view is that any browser-to-local communication must carry major risks. The other view is that it is just a routine installation configuration and deserves no special attention. A more accurate judgment is this: the risk does not come from the communication channel itself, but from whether registration is transparent, permissions are minimal, and data handling is auditable.

Native Messaging is the standard communication mechanism between browser extensions and local native programs. By itself, it is only a controlled message channel. It does not automatically read webpage content, cookies, local storage, or system passwords. What really matters is whether the installation process clearly informs the user, whether the extension has only the necessary permissions, whether the local native program has been granted excessive privileges, and whether there is any undocumented data transmission behavior.

2. What Is Native Messaging in Browser Extensions?

Native Messaging is a mechanism provided by mainstream browser engines for bidirectional message exchange between browser extensions and local native programs running on the operating system. Browser extensions usually run in a sandbox and cannot directly access operating system resources. Local native programs have higher privileges, but they should not arbitrarily read internal browser data. Native Messaging provides a controlled link between the two.

A typical workflow is as follows:

1. When the local native program is installed, it writes a manifest file to a specified location in the operating system. This file is usually called a Native Messaging Host Manifest.
2. The manifest declares the host name, the executable path, and the identifiers of the browser extensions that are allowed to connect.
3. When a matching extension initiates a connection, the operating system launches the corresponding local native program.
4. The browser and the native program communicate through standard input and output. A common message format is a length-prefixed JSON message.

Example manifest:

{
  "name": "com.example.native_host",
  "description": "Example Native Messaging host",
  "path": "/usr/local/bin/native_host",
  "type": "stdio",
  "allowed_origins": ["chrome-extension://<extension-id>/"]
}

The allowed_origins field binds the extensions that are allowed to connect to the native host. If this field is configured too broadly, has an unknown source, or is unrelated to the actual business use case, it may expand the communication exposure surface.

3. Common Questions: Risks and How to Check

What is Native Messaging?
Native Messaging is a controlled message channel between browser extensions and local native programs. It is commonly used for scenarios such as local file processing, device access, and debugging assistance.

What are the risks?
The risks are mainly concentrated in three areas: insufficient notification to the user during installation; excessive extension permissions; and local native programs reading browser configuration or sensitive system data, potentially followed by undocumented data transmission.

How can registered hosts be checked?
You can inspect Native Messaging Host manifest files through operating system directories, registry entries, or file auditing. Focus on the manifest path, source, modification time, and whether allowed_origins or allowed_extensions are clear, necessary, and consistent with the expected use case.

4. Transparency of Registration: The Key Is Sufficient Disclosure, Not Bypassing Prompts

Native Messaging Host registration is usually completed by an installer writing a manifest file or registry entry. When an extension initiates a connection, browsers usually do not show a confirmation prompt for every connection. Therefore, the key security issue is not whether a browser prompt was bypassed. It is whether the installation process clearly informs the user that the system will add a local communication host, which extensions are allowed to connect, whether the capability is necessary, and whether it can be disabled.

If an installer silently writes configuration without giving the user a clear explanation, it may create a situation where a feature is enabled but the user is unaware of it. A manifest itself does not equal malicious behavior. However, if it is used to establish a long-lived communication channel that is not required by the business and not known to the user, it should be treated as a high-risk configuration.

A reasonable design should include: a prompt before installation, visibility into the enabled state, an explanation of the permission scope, and a way for the user to disable or revoke it. When ordinary users encounter an unfamiliar Native Messaging Host file, they should not focus only on the file name. They should also check its source, path, signer information, and recent modification time.

5. What Data Can Be Accessed After a Successful Handshake: Separate Channel Capability From Extension Permissions

It is important to emphasize: the Native Messaging channel itself does not automatically read the DOM, cookies, LocalStorage, SessionStorage, or browser fingerprint. Whether these data may be accessed depends on three conditions: the permissions held by the extension, whether extension scripts run on the relevant pages, and whether the local native program has been granted permission to access browser configuration files or system data.

Data or Capability	Source	Additional Condition Required	Risk Level	Mitigation Action
DOM and page content	Content scripts, page scripts, extension permissions	Requires the extension to have page access permissions	High	Grant only necessary page permissions and review extension behavior
Cookies	Extension-related APIs, request interception capabilities	Requires extension permissions; it is not automatically read by the channel	High	Avoid reading unrelated cookies and prefer short-lived tokens
LocalStorage / SessionStorage	Page scripts or extension scripts	Requires page or script access permissions	Medium	Control script injection scope and avoid site-wide reading
Browser fingerprint	Extension scripts; local programs reading browser or system information	Depends on extension permissions and local program privileges	Medium	Minimize data collection and do not collect unrelated environment information
Password manager plaintext	Extension or local native program	Extensions usually cannot read it directly; a local native program may access some protected storage depending on the system keychain, credential manager, and user unlock state	High	Do not request, read, or transmit password-type data

Regarding password managers, a more accurate statement is needed: extensions usually cannot directly read plaintext passwords from operating-system-level password managers, but a local native program running with user privileges may access some protected storage. The actual outcome depends on the system keychain, credential manager, and whether the user has unlocked the relevant storage. Therefore, it is incorrect to assume that reading is definitely impossible, and it is also incorrect to assume that any installation can read such data. The effective approach is to limit local native program privileges, review access to sensitive directories, and avoid unnecessary access to credential data.

In other words, desktop applications and browser accounts are not two naturally isolated systems. If extension permissions are too broad, local native program privileges are too high, or the two exchange data through Native Messaging in an uncontrolled manner, a covert data path may be formed.

6. User Marking and Covert Transmission: Risk Identification Only, No Implementation Details

Another common concern is “marking users and sending data back.” Browser fingerprinting itself is a set of technical characteristics used to identify an environment, including time zone, language, screen resolution, fonts, hardware features, and other information. Combining some of this information may, in theory, allow rough inference about a user’s location or device environment. This type of capability may be reasonable when used for security risk control. However, if it is used to build profiles without user awareness, it may cross a privacy boundary.

More concerning is the risk of covert transmission. Some programs may try to hide marking or identification information inside content that appears normal, such as ordinary request parameters, metadata fields, image resources, font files, or telemetry data. From a defensive perspective, the essence of this risk is that content which appears harmless may actually carry hidden information and increase the difficulty of auditing.

This article only describes such scenarios from a risk identification perspective and does not provide any specific implementation details. For ordinary users, the focus should not be on studying steganography techniques. Instead, they should check whether software makes abnormal network requests, whether it reads browser data unrelated to its business function, and whether it continuously transmits information without a privacy explanation.

7. Prevention Checklist for Developers and Users

Five Principles for Developers

1. Transparent registration: When installing a Native Messaging Host, clearly inform the user about the communication capability to be established and provide an option to disable it.
2. Least privilege: allowed_origins or allowed_extensions should be strictly bound to the extensions that are truly needed. Avoid broad authorization.
3. Data minimization: After the handshake, transmit only business-necessary data. Do not casually collect unrelated sensitive information such as cookies, fingerprints, or page content.
4. Auditable transmission: Any data transmission should have a clear privacy statement. Avoid covert encoding, vague naming, or other techniques that cannot be audited.
5. User control: Provide users with entry points to view, disable, and revoke communication authorization so they can understand and manage it at any time.

User Checklist

Common Windows locations:
Check whether the registry contains NativeMessagingHosts entries related to Chrome, Edge, or Firefox. Examples include:

• HKLM\SOFTWARE\Google\Chrome\NativeMessagingHosts
• HKCU\SOFTWARE\Google\Chrome\NativeMessagingHosts
• HKLM\SOFTWARE\Microsoft\Edge\NativeMessagingHosts
• HKLM\SOFTWARE\Mozilla\NativeMessagingHosts

Registry values usually point to a JSON manifest file. Open the referenced file and review its contents and source.

Common macOS locations:
Check these locations:

• /Library/Application Support/Google/Chrome/NativeMessagingHosts/
• ~/Library/Application Support/Google/Chrome/NativeMessagingHosts/
• The corresponding NativeMessagingHosts folders for Edge and Firefox.

Common Linux locations:
Check these locations:

• ~/.config/google-chrome/NativeMessagingHosts
• ~/.config/chromium/NativeMessagingHosts
• ~/.config/microsoft-edge/NativeMessagingHosts
• ~/.mozilla/native-messaging-hosts
• /usr/lib/mozilla/native-messaging-hosts

Audit points:
Inspect the manifest fields name, path, description, allowed_origins, and allowed_extensions. Be cautious if the path points to an unknown program, the description is vague, or the bound extension does not match the actual software.

Revocation:
If a Native Messaging Host is unnecessary or its source is unclear, you can uninstall the related software, delete or disable the corresponding manifest, remove the related extension, and check startup items and local native program permissions. For enterprise environments, investigation should also be combined with file integrity auditing, endpoint privilege management, and network egress log review.

8. Conclusion

Native Messaging between browsers and desktop applications is a double-edged sword. It can help developers implement local integration, but it can also become a data collection or covert monitoring channel when transparency and constraints are lacking. For developers, maintaining the principles of informed consent, data minimization, and auditability is the foundation for earning user trust. For users, understanding these mechanisms, regularly checking registered hosts, and maintaining a necessary level of scrutiny are important forms of self-protection in the digital age.