Browser Use allows bypassing `allowed_domains` by putting a decoy domain in http auth username portion of a URL

### Summary During a manual source code review, [**ARIMLABS.AI**](https://arimlabs.ai) researchers identified that the `browser_use` module includes an embedded whitelist functionality to restrict URLs that can be visited. This restriction is enforced during agent initialization. However, it was discovered that these measures can be bypassed, leading to severe security implications. ### Details **File:** `browser_use/browser/context.py` The `BrowserContextConfig` class defines an `allowed_domains` list, which is intended to limit accessible domains. This list is checked in the `_is_url_allowed()` method before navigation: ```python @dataclass class BrowserContextConfig: """ [STRIPPED] """ cookies_file: str | None = None minimum_wait_page_load_time: float = 0.5 wait_for_network_idle_page_load_time: float = 1 maximum_wait_page_load_time: float = 5 wait_between_actions: float = 1 disable_security: bool = True browser_window_size: BrowserContextWindowSize = field(default_factory=lambda: {'width': 1280, 'height': 1100}) no_viewport: Optional[bool] = None save_recording_path: str | None = None save_downloads_path: str | None = None trace_path: str | None = None locale: str | None = None user_agent: str = ( 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.102 Safari/537.36' ) highlight_elements: bool = True viewport_expansion: int = 500 allowed_domains: list[str] | None = None include_dynamic_attributes: bool = True _force_keep_context_alive: bool = False ``` The _is_url_allowed() method is responsible for checking whether a given URL is permitted: ```python def _is_url_allowed(self, url: str) -> bool: """Check if a URL is allowed based on the whitelist configuration.""" if not self.config.allowed_domains: return True try: from urllib.parse import urlparse parsed_url = urlparse(url) domain = parsed_url.netloc.lower() # Remove port number if present if ':' in domain: domain = domain.split(':')[0] # Check if domain matches any allowed domain pattern return any( domain == allowed_domain.lower() or domain.endswith('.' + allowed_domain.lower()) for allowed_domain in self.config.allowed_domains ) except Exception as e: logger.error(f'Error checking URL allowlist: {str(e)}') return False ``` The core issue stems from the line `domain = domain.split(':')[0]`, which allows an attacker to manipulate basic authentication credentials by providing a username:password pair. By replacing the username with a whitelisted domain, the check can be bypassed, even though the actual domain remains different. ### Proof of Concept (PoC) Set allowed_domains to ['example.com'] and use the following URL: https://example.com:pass@localhost:8080 This allows bypassing all whitelist controls and accessing restricted internal services. ### Impact - Affected all users relying on this functionality for security. - Potential for unauthorized enumeration of localhost services and internal networks. - Ability to bypass domain whitelisting, leading to unauthorized browsing.