CVE-2026-16771

Executive Summary

CVE-2026-16771 describes a critical authentication bypass vulnerability affecting the Arris BGW210-700 residential gateway in firmware versions 2.7.7 and earlier. The device's /cgi-bin/*.ha management endpoints enforce no server-side authentication, relying exclusively on client-side CSS/JavaScript gating that any HTTP client can trivially bypass. An unauthenticated attacker with LAN access can read sensitive configuration data, modify persistent device settings, or trigger backend diagnostic operations. The vulnerability carries a CVSS score of 8.8 (High) with a full confidentiality, integrity, and availability impact triad. The issue is systemic across the CGI handler chain, suggesting a fundamental architectural flaw rather than an isolated endpoint misconfiguration. No public exploit code or PoC is currently available, and the CVE is not listed in CISA's Known Exploited Vulnerabilities catalog.

Technical Analysis

The Arris BGW210-700 is a broadband gateway device commonly deployed by ISPs for residential fiber and DSL internet service. The vulnerable component is the embedded CGI management interface, accessible via HTTP on the local network.

The vulnerability class is CWE-306 — Missing Authentication for Critical Function. The NVD description indicates that the firmware's /cgi-bin/*.ha handler chain performs no server-side authentication verification whatsoever. Instead, the intended security control is implemented entirely on the client side, using CSS/JavaScript to visually hide or disable management controls from unauthenticated users. This is a fundamental security design flaw: client-side gating is a user-interface convenience, not a security boundary.

The attack mechanism is straightforward. Any HTTP client — including curl, wget, Python's requests library, or a raw socket connection — can issue requests directly to /cgi-bin/*.ha endpoints without supplying credentials or session tokens. The server processes these requests as if they were authorized, because no authentication check exists in the request-handling path. The client-side CSS/JavaScript gating is only applied to the rendered HTML interface; it has zero effect on programmatic HTTP traffic.

The phrase "systemic across the CGI handler chain" indicates that the authentication omission is not confined to a single script. Rather, the entire family of CGI handlers matched by the /cgi-bin/*.ha glob pattern shares this defect. This suggests that authentication was either implemented at a wrapper level that was never invoked, or was simply never built into the CGI dispatch architecture.

The attack surface is the LAN-facing HTTP management interface. Given the CVSS vector AV:A (Adjacent Network), exploitation requires the attacker to be on the same Layer 2 network segment as the device. This includes other devices on the home LAN, a compromised IoT device, or a rogue wireless client (if the attacker can associate with the gateway's Wi-Fi). The attack complexity is Low, privileges are None, and no user interaction is required.

Specific technical details regarding which configuration parameters can be read or modified, which diagnostic operations can be triggered, and the exact structure of the CGI request handlers are not disclosed in the NVD description. Insufficient technical detail is available to enumerate specific function names, parameter names, or backend operations beyond the general class of actions described (read configuration, modify settings, trigger diagnostics).

Exploitation Scenarios

No public PoC or exploit code is available. The attack chain below is inferred from the vulnerability class and the NVD description.

Step 1 — Reconnaissance and Target Identification: The attacker, already on the victim's LAN (or having compromised a device on that LAN), performs a network scan to identify the gateway. The Arris BGW210-700 typically uses a predictable management IP address (commonly 192.168.0.1 or 10.0.0.1). The attacker can confirm the device identity by requesting the root page and examining the HTTP response headers or the HTML title for Arris branding.

Step 2 — Vulnerability Trigger: The attacker identifies the /cgi-bin/*.ha endpoint family. Without supplying any authentication credentials, session cookie, or CSRF token, the attacker issues an HTTP GET request directly to one of these management endpoints. Because the server performs no server-side authentication, the request is processed as legitimate.

Step 3 — Payload/Execution: At the vulnerability-class level, the attacker crafts HTTP requests to invoke CGI handler functionality. For a configuration-read operation, simple HTTP GET requests to the relevant endpoints would suffice. For modification operations, HTTP POST requests with form-encoded or query-string parameters would be sent to the CGI handlers. Since any HTTP client can be used, tooling such as curl, Burp Suite, or a short Python script is sufficient. No special payload obfuscation or evasion is needed, as no authentication check exists to bypass at the protocol level.

Step 4 — Post-Exploitation Impact: Post-exploitation actions available to the attacker align with the CIA triad reflected in the CVSS score:

• Confidentiality (High): Read sensitive configuration data, including ISP credentials, PPPoE username/password (if stored in plaintext), Wi-Fi pre-shared keys, and network topology details.
• Integrity (High): Modify persistent device settings — e.g., change the administrator password (locking out the legitimate owner), alter DNS settings (enabling DNS rebinding or sinkholing), disable firewall rules, or change Wi-Fi security settings.
• Availability (High): Trigger backend diagnostic operations that could cause the device to crash, reboot repeatedly, or enter a non-functional state. A full factory reset could disconnect the household entirely.

Impact Assessment

CVSS v3.1 Score: 8.8 (High) — Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

The adjacent-network attack vector (AV:A) is the principal limiting factor; the attacker must be on the local network segment. However, this constraint is frequently satisfied in practice: home gateways are shared infrastructure accessed by all devices in a household, and a single compromised IoT device or open Wi-Fi network expands an attacker's reach to include the gateway.

The business impact depends on deployment context. For residential users, the primary risks are loss of home network control, credential theft, and denial of service. For enterprise or remote-work environments where BGW210-700 units are used as customer-premises equipment for branch offices or teleworkers, the impact escalates: an attacker who controls the gateway can intercept unencrypted traffic, redirect DNS, or maintain persistent access to the network edge.

The broad exploitability characteristics (AC:L, PR:N, UI:N) make this vulnerability highly likely to be weaponized, even though no exploit is public today. The EPSS score of 0.00352 (28.3rd percentile) indicates a low current probability of exploitation in the wild — consistent with the absence of public PoC material. However, the CVE publication itself lowers the barrier for threat actors and security researchers to discover the trivial bypass mechanism.

The systemic nature of the flaw across the entire CGI handler chain means that the entire management interface is compromised — this is not a single misbehaving endpoint but a broken authentication architecture across all management functionality.

Detection Guidance

Sigma Rule

title: Arris BGW210-700 Unauthenticated CGI Management Access
id: 5f7a2c1e-8d4b-4c9a-b6e2-7b5f0d8a3c91
status: experimental
description: Detects HTTP requests to Arris BGW210-700 /cgi-bin/*.ha management endpoints lacking authentication headers or session indicators, indicating potential CVE-2026-16771 exploitation.
author: Valtersit Threat Intelligence
date: 2026/05/15
logsource:
  category: webserver
  product: arris
  service: http
detection:
  selection:
    cs-method:
      - 'GET'
      - 'POST'
    cs-uri-extension:
      - '.ha'
    cs-uri-path:
      - '/cgi-bin/*'
    sc-status:
      - 200
      - 302
  filter_authenticated:
    cs-cookie|contains:
      - 'session'
      - 'auth'
      - 'token'
    cs-user-agent|contains:
      - 'Mozilla'
  condition: selection and not filter_authenticated
level: critical
falsepositives:
  - Misconfigured legitimate management tools
  - Authorized unauthenticated diagnostic endpoints (if any exist after patching)
fields:
  - client_ip
  - cs_uri_path
  - cs_method
  - sc_status
tags:
  - attack.initial_access
  - attack.t1190
  - cve.2026.16771

YARA Rule

rule CVE_2026_16771_Arris_BGW210_CGI_Bypass {
    meta:
        author = "Valtersit Threat Intelligence"
        description = "Detects strings and patterns associated with Arris BGW210-700 /cgi-bin/*.ha unauthenticated access attempts or exploit tooling"
        date = "2026-05-15"
        reference = "CVE-2026-16771"
        severity = "critical"
    strings:
        $ha_endpoint = "/cgi-bin/" ascii wide
        $ha_ext = ".ha" ascii wide
        $gw_model = "BGW210-700" ascii wide
        $gw_model2 = "bGW210" ascii wide nocase
        $config_read = "config" ascii wide nocase
        $diagnostic = "diagnos" ascii wide nocase
        $setting_mod = "setting" ascii wide nocase
    condition:
        uint16(0) == 0x5A4D or uint32(0) == 0x464c457f
        and 2 of ($ha_endpoint, $ha_ext, $gw_model, $gw_model2)
        and 1 of ($config_read, $diagnostic, $setting_mod)
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-16771 Arris BGW210-700 Unauthenticated CGI Management Access Attempt"; flow:to_server,established; http.uri; content:"/cgi-bin/"; http.uri; content:".ha"; http.uri; endswith; http.method; content:"GET"; http.method_nocase; content:"POST"; pcre:"/^\/cgi-bin\/[^\s]*\.ha\b/Hi"; reference:cve,2026-16771; classtype:attempted-admin; sid:10016771; rev:1;)

Elastic Detection

sequence by source.ip with maxspan=5m
  [network where destination.port == 80 and
   network.direction == "egress" and
   url.path matches "/cgi-bin/*.ha"
   and not url.scheme == "https"]
  [http where request.method in ("GET", "POST") and
   url.path matches "/cgi-bin/*.ha" and
   not request.headers.cookie like "*session*" and
   not request.headers.cookie like "*auth*" and
   not request.headers.authorization is not null]

Splunk SPL Query

index=* sourcetype=access_combined OR sourcetype=stream:http
| where like(uri_path, "%/cgi-bin/%.ha%")
| where NOT (cookie LIKE "%session%" OR cookie LIKE "%auth%" OR cookie LIKE "%token%")
| eval exploitation_attempt = if(method IN ("GET","POST"), "probable", "potential")
| stats count by src_ip, uri_path, method, status, exploitation_attempt
| where count > 3
| sort - count
| table _time, src_ip, uri_path, method, status, count, exploitation_attempt

Wazuh OSSEC Rule

<group name="local,L2_sec,PCI_DSS_10.6.1,">
    <rule id="10016771" level="14">
        <if_sid>31100</if_sid>
        <match>/cgi-bin/</match>
        <match>.ha</match>
        <regex>HTTP/1.1</regex>
        <description>Arris BGW210-700 unauthenticated CGI management access attempt (CVE-2026-16771)</description>
        <group>authentication_failure,attack.initial_access,</group>
        <mitre>
            <id>T1190</id>
        </mitre>
    </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 2/4 — CLAIMED A patch is claimed to exist by the CNA (Arris/certcc), but this has not been independently confirmed by a second source. No specific patched version number, advisory identifier, or download link has been published. Exercise caution and verify fix availability directly with Arris or your ISP before relying on it.

Immediate Mitigations (apply first):

1. Restrict management interface access: If the device supports firewall rules or access-control lists, restrict access to the management HTTP port (typically 80) to a single trusted administration host only.
2. Disable remote/cloud management: Many Arris gateways expose cloud-based or WAN-side management. If CVE-2026-16771 is exploitable over the WAN (not confirmed — likely LAN/adjacent only), disable all remote management features immediately.
3. Segment the network: Place IoT devices on a separate VLAN or guest network so that a compromised IoT device cannot reach the gateway's management interface.
4. Monitor management traffic: Deploy the detection rules above on network taps, gateway syslog output (if available), or upstream router/firewall logs to identify anomalous HTTP requests to the gateway.

Patch/Upgrade Steps:

1. Contact your ISP — the BGW210-700 is ISP-managed equipment in most deployments. Ask the ISP to push the patched firmware when available and to confirm the patched version number.
2. If the device is directly owned/operated, check the Arris support portal or the vendor advisory (when published) for a firmware update above version 2.7.7.
3. After updating, verify the fix by attempting an unauthenticated HTTP request to a /cgi-bin/*.ha endpoint from an external HTTP client — the request should be rejected with an authentication challenge or 401/403 status.
4. If the claimed patch is not verifiable, treat the device as persistently vulnerable.

Long-Term Hardening:

1. Replace end-of-life equipment: If Arris does not deliver a confirmed patch, plan replacement of the BGW210-700 with a current-generation gateway that enforces server-side authentication on all management endpoints.
2. Disable unnecessary services: Turn off any unused services (WPS, UPnP, remote diagnostics) exposed on the LAN or WAN interface.
3. Change default administrative credentials on any remaining unpatched device.
4. Establish a routine firmware update cadence for all network edge equipment.
5. Monitor CISA KEV: Though CVE-2026-16771 is not currently on CISA's Known Exploited Vulnerabilities list, re-check periodically and prioritize patching if it is added.

References

1. NVD Entry — CVE-2026-16771: https://nvd.nist.gov/vuln/detail/CVE-2026-16771
2. Arris Vendor Advisory (claimed patch source, not yet independently confirmed): Refer to Arris official support portal for BGW210-700 firmware release notes.
3. CWE-306 Missing Authentication for Critical Function: https://cwe.mitre.org/data/definitions/306.html
4. CISA Known Exploited Vulnerabilities Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog (CVE-2026-16771 not currently listed)

No known threat-actor campaigns, exploit-in-the-wild evidence, or public exploit code exists for CVE-2026-16771 at the time of writing. The lack of public PoC material and the EPSS score in the low percentile suggest that this vulnerability has not yet been actively targeted; however, the trivial bypass mechanism and high severity make weaponization likely once the vulnerability becomes more widely known.