What is check-browser-hijack?

A command that checks installed web browsers for browser hijacking, where unwanted software changes the homepage, search engine, or extensions. It examines settings and extension files in Chrome, Firefox, Edge, Internet Explorer, Brave, and Opera.

Use it to inspect browser preferences, search providers, homepages, installed extensions, extension developers, permissions, and suspicious URLs.

It helps find unauthorized browser changes that can redirect searches, alter startup pages, or add unsafe extensions. The checks point to specific settings and extension permissions that may reveal the problem.

check-browser-hijack — Command by DeepBitsTechnology

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods

npx agentmods add commands/deepbitstechnology/claude-plugins/check-browser-hijack

Clone the repo

git clone --depth 1 https://github.com/DeepBitsTechnology/claude-plugins

Per session 21 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.

When invoked 1,034 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. Scan, not verified.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5	$0.00021	$0.01034
Opus 5	$0.00010	$0.00517
Sonnet 5	$0.00004	$0.00207
Haiku 4.5	$0.00002	$0.00103

Measured 2d ago against content hash ff04a69f7640, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

check-browser-hijack scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

drbinary-chat-plugin/commands/check-browser-hijack.md · 174 lines

How it starts

The opening of the file, as written. The whole thing — 174 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Browser Hijacking Detection

Scan all installed browsers for signs of hijacking, unauthorized modifications, and malicious extensions.

Browsers to Check

Google Chrome
Mozilla Firefox
Microsoft Edge
Internet Explorer
Brave
Opera

Detection Areas

1. Browser Settings Files

Check for unauthorized modifications in:

Chrome

%LOCALAPPDATA%\Google\Chrome\User Data\Default\Preferences
%LOCALAPPDATA%\Google\Chrome\User Data\Default\Secure Preferences
Look for: homepage_url, default_search_provider, homepage

Firefox

%APPDATA%\Mozilla\Firefox\Profiles\*.default*\prefs.js
Look for: browser.startup.homepage, browser.search.defaultenginename

Edge

%LOCALAPPDATA%\Microsoft\Edge\User Data\Default\Preferences
Similar structure to Chrome

2. Browser Extensions

Scan extension directories:

Chrome Extensions

%LOCALAPPDATA%\Google\Chrome\User Data\Default\Extensions\
Check for unknown or suspicious extension IDs
Review extension manifest.json files for:
- Excessive permissions
- Unknown developers
- Suspicious URLs

Firefox Add-ons

%APPDATA%\Mozilla\Firefox\Profiles\*.default*\extensions\
Review extensions.json

Edge Extensions

%LOCALAPPDATA%\Microsoft\Edge\User Data\Default\Extensions\

3. Browser Shortcuts

Check desktop and taskbar shortcuts for hijacking:

# Check Chrome shortcut target
Get-ItemProperty "C:\Users\*\Desktop\*.lnk" | Select-Object Target

Look for modified targets with:

Suspicious command line arguments
URLs appended to shortcuts
Redirects to unwanted sites

4. Registry Browser Settings

# IE/Edge HomePage
HKCU:\Software\Microsoft\Internet Explorer\Main -> "Start Page"

# Default search providers
HKCU:\Software\Microsoft\Internet Explorer\SearchScopes

# Browser policies
HKCU:\Software\Policies\Microsoft\Edge
HKCU:\Software\Policies\Google\Chrome

5. Proxy Settings

Check for unauthorized proxy configurations:

HKCU:\Software\Microsoft\Windows\CurrentVersion\Internet Settings

Look for:

ProxyEnable = 1 (when not expected)
ProxyServer settings
AutoConfigURL (PAC file hijacking)

Read the full file on GitHub · 174 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

2d ago First seen · 174 lines · 21 tokens per session scan A ff04a69f7640

Subscribe to this mod's changes

check-browser-hijack is a command published in the GitHub repository DeepBitsTechnology/claude-plugins (47 stars, last pushed 1mo ago), licensed Apache-2.0. It adds 21 tokens to every session and 1,034 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

Browser automation Research binary-analysis claude-code-plugin cybersecurity-tools incident-response malware-analysis vulnerability-assessment

check-browser-hijack