Software Engineering Institute

Overview

Firmware versions 2.7.7 and earlier of the Arris BGW210-700 residential gateway contain an authentication bypass vulnerability, tracked as CVE-2026-16771, that allows any unauthenticated LAN-side user to read sensitive configuration data and modify device settings through web management endpoints. Although this vulnerability was recently discovered, the majority of in-service gateways are not expected to be running the affected version. Only devices that have not received automated ISP-managed firmware updates since version 2.7.7 in 2020 are vulnerable.

Description

The Arris BGW210-700 is a residential gateway used widely in AT&T deployments to provide routing, wireless networking, and wide-area network (WAN) connectivity for home users. The device exposes a browser-based management interface on the local-area network (LAN) side that allows users to configure WiFi settings, check diagnostics, and run system operations.

Several CGI (Common Gateway Interface) handlers within the BGW210-700's web interface do not enforce any server-side authentication checks. Although the interface presents an "Access Code" prompt to users, this restriction is entirely implemented through client-side HTML and JavaScript and is not validated by the server before processing requests. As a result, any HTTP client that ignores client-side code can directly access and interact with the underlying CGI endpoints.

The lack of server-side authentication affects multiple configuration and diagnostic pages. The wconfig_unified.ha endpoint returns the plaintext WiFi pre-shared key for all configured SSIDs to any unauthenticated requester. The broadbandconfig.ha endpoint accepts unauthenticated POST requests that directly modify WAN configuration parameters, including settings that persist across device reboots. Additional diagnostic endpoints, such as diag.ha, allow unauthenticated triggering of backend diagnostic jobs.

Impact

This vulnerability allows any unauthenticated user on the LAN, including devices connected to the gateway through the main WiFi network, Guest WiFi network, or LAN ethernet, to read sensitive configuration information and make persistent changes to gateway settings. A local attacker can retrieve the network's plaintext WiFi password with a single HTTP request and achieve unauthorized access to manipulate, intrude on, and interfere with protected networks.

Solution

This gateway is ISP-managed, so all standard internet-connected devices are expected to have been automatically updated to newer unaffected versions. Users can determine their active version by checking their router's diagnostic settings via web browser, and optionally contact their ISP to confirm that automatic updates are functioning correctly. Because the vulnerability is limited to the LAN-side management interface, standard network hygiene practices such as isolating untrusted devices, keeping IoT systems updated, and monitoring for the presence of unknown clients can further reduce risk in environments where older firmware may still be present.

Acknowledgements

Thanks to David Weekly for researching and reporting this vulnerability. This document was written by Molly Jaconski.

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