Arris BGW210-700 gateway auth bypass flaw
An authentication bypass in old Arris BGW210-700 firmware lets any LAN user read WiFi passwords and modify gateway settings without credentials.
Sourcekb.cert.org — open the original
What to check
- Applies to
- The 1 CVE named below. Whether you run an affected version is not assessed: check the versions the source lists.
- Exploitation
- No exploitation in the wild and no public exploit is recorded for the CVEs named.
CERT/CC disclosed CVE-2026-16771, an authentication bypass affecting Arris BGW210-700 residential gateways running firmware 2.7.7 or earlier, a device widely deployed by AT&T for home internet service. Several CGI-based web management endpoints, including wconfig_unified.ha, broadbandconfig.ha, and diag.ha, fail to perform any server-side authentication check. The device's "Access Code" prompt is enforced only through client-side HTML/JavaScript, meaning any HTTP client that bypasses the browser UI can interact directly with these backend endpoints.
The practical impact is significant at the individual device level: any unauthenticated LAN-side user, including guests on WiFi or wired clients, can retrieve the plaintext WiFi pre-shared key with a single HTTP request, and can send POST requests to persistently alter WAN configuration or trigger diagnostic jobs. This gives a local attacker full visibility into and control over the home network's wireless credentials and gateway configuration without needing to authenticate.
Exploitation is limited in scope because it requires LAN access, and the affected firmware version dates to 2020; since the device is ISP-managed, most in-service units have since received automatic updates and are not expected to be vulnerable. Only gateways that have not received an update since 2.7.7 remain exposed. CERT/CC recommends users verify their firmware version and confirm automatic updates are functioning, alongside standard LAN hygiene such as isolating untrusted devices and monitoring for unknown clients.
Mentioned in this report
Source reporting: https://kb.cert.org/vuls/id/141367
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