CVE-2026-16771 Overview
CVE-2026-16771 is a missing authentication vulnerability [CWE-306] in the Arris BGW210‑700 residential gateway. Firmware versions 2.7.7 and earlier fail to enforce any server-side authentication on /cgi-bin/*.ha management endpoints. The device relies solely on client-side CSS and JavaScript to gate access to administrative functions. Any HTTP client on the LAN can bypass this control by issuing direct requests to the CGI handlers. Attackers can read sensitive configuration data, modify persistent device settings, and trigger backend diagnostic operations without credentials. The issue is systemic across the CGI handler chain rather than isolated to a single endpoint.
Critical Impact
Unauthenticated adjacent-network attackers can fully read and modify gateway configuration by sending direct HTTP requests to CGI endpoints.
Affected Products
- Arris BGW210‑700 gateway firmware version 2.7.7
- Arris BGW210‑700 gateway firmware versions earlier than 2.7.7
- CGI management interface at /cgi-bin/*.ha
Discovery Timeline
- 2026-07-28 - CVE-2026-16771 published to NVD
- 2026-07-28 - Last updated in NVD database
Technical Details for CVE-2026-16771
Vulnerability Analysis
The Arris BGW210‑700 exposes an HTTP-based management interface backed by CGI handlers under /cgi-bin/. Endpoint names use the .ha extension. The web UI restricts navigation and form submission using client-side controls implemented in CSS and JavaScript. The backend CGI handlers never independently verify that a request originated from an authenticated session.
An attacker on the local area network can send crafted HTTP requests directly to any .ha endpoint using a command-line HTTP client or scripting library. The gateway processes those requests as if they came from an authorized administrator. This exposes configuration read, configuration write, and diagnostic execution paths to unauthenticated callers on the adjacent network.
Root Cause
The root cause is Missing Authentication for Critical Function [CWE-306]. Authentication enforcement lives entirely in the browser-rendered UI. Server-side handlers accept requests without verifying session cookies, tokens, or credentials. The trust boundary is drawn at the browser instead of the CGI handler, which violates standard access control design for network-facing management interfaces.
Attack Vector
Exploitation requires network adjacency, typically a wired or wireless client on the gateway's LAN segment. The attacker sends direct HTTP requests to endpoints such as /cgi-bin/*.ha, bypassing the JavaScript-driven login flow. No credentials, user interaction, or prior compromise is required. Successful requests can retrieve provisioning data, alter persistent settings, or invoke diagnostic routines that affect device behavior. Refer to the CERT Vulnerability Advisory #141367 for technical details on the affected endpoints.
Detection Methods for CVE-2026-16771
Indicators of Compromise
- HTTP requests to /cgi-bin/ endpoints ending in .ha from LAN hosts that never loaded the gateway's login page
- Unexpected configuration changes on the BGW210‑700, including altered DNS, port forwarding, or firewall rules
- Diagnostic operations triggered outside of scheduled maintenance windows
- HTTP requests to gateway management endpoints lacking valid session cookies
Detection Strategies
- Monitor network flows to the gateway management IP for direct CGI requests that skip the standard login navigation sequence
- Baseline gateway configuration and alert on drift in DHCP, DNS, firewall, and remote management settings
- Inspect HTTP User-Agent strings targeting the gateway for non-browser clients such as curl, python-requests, or wget
Monitoring Recommendations
- Capture LAN-side HTTP traffic destined for the gateway and retain access logs where available
- Correlate new device joins on the LAN with subsequent management-plane requests within short time windows
- Track outbound traffic patterns from the gateway for signs of altered routing or DNS behavior after suspected configuration changes
How to Mitigate CVE-2026-16771
Immediate Actions Required
- Apply firmware updates from the service provider once available; contact the ISP that provisioned the BGW210‑700
- Restrict LAN access to the gateway management interface using client isolation and segmented VLANs where supported
- Change any shared LAN passphrase to limit which devices reach the management network
- Audit current gateway configuration for unauthorized changes to DNS, port forwarding, and remote administration settings
Patch Information
No vendor patch is referenced in the NVD entry at publication. Because the BGW210‑700 is typically deployed and updated by internet service providers, firmware distribution is controlled upstream. Consult the CERT Vulnerability Advisory #141367 for the current vendor coordination status and any interim guidance.
Workarounds
- Place the BGW210‑700 in bridge or passthrough mode behind a separately administered router that enforces its own access controls
- Block untrusted wired ports and disable open Wi-Fi access to reduce the population of hosts able to reach the management endpoints
- Disable remote management features and confirm the WAN-side interface does not expose /cgi-bin/ handlers
- Monitor the LAN for unauthorized HTTP clients targeting the gateway address
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
