CVE-2026-111712

Executive Summary

CVE-2026-111712 is an authentication bypass vulnerability (CWE-288: Authentication Bypass Using an Alternate Path or Channel) affecting Netcore NR256CN routers through firmware version 1.5.140116. Unauthenticated remote attackers can reach protected management CGI handlers by prefixing request URIs with a publicly accessible route such as l7_web_auth.cgi or an .ico path, effectively circumventing web authentication controls. A successful exploitation grants access to administrative functionality, enabling configuration manipulation and potential network-adjacent lateral movement, though direct confidentiality and integrity impacts are scored as Low (CVSS 6.5).

Technical Analysis

The vulnerability resides in the web-based authentication architecture of the Netcore NR256CN router. The device's HTTP server exposes a routing mechanism where access control decisions are applied based on the URI path. The l7_web_auth.cgi endpoint and certain .ico resource routes are treated as public (unauthenticated) by design — likely because the authentication CGI itself must be reachable by browsers during the login flow, and favicon/icon requests are commonly served without session validation.

The flaw class described — CWE-288, "Authentication Bypass Using an Alternate Path or Channel" — indicates that the path-matching logic governing access control performs prefix matching against public routes in a manner that can be subverted. By constructing a request whose URI begins with a whitelisted prefix (e.g., l7_web_auth.cgi or an .ico asset path) but which still resolves to a protected management CGI handler, an attacker can coax the router into processing administrative actions without any credential check. This is a classic "path confusion" pattern: the authorization gate inspects the beginning of the URI and short-circuits its check, while the downstream CGI dispatcher resolves the request to a privileged handler.

Key technical observations from the available data:

• The bypass is network-reachable (AV:N) and requires no privileges (PR:N) or user interaction (UI:N), yielding the full 6.5 base score.
• Attack complexity is Low (AC:L), implying the bypass does not require a race condition, brute force, or complex state manipulation.
• Scope is Unchanged (S:U) — the attacker impacts the router as the sole security authority; the described flaw does not by itself pivot the vulnerable component's authority to other components.
• Confidentiality and Integrity are both Low (C:L/I:L), suggesting the protected handlers likely expose configuration data and allow limited modification, while Availability is None (A:N).

The public-route whitelist specifically referenced in the advisory (l7_web_auth.cgi, .ico) is the most probable attack surface. Specific handler names, internal dispatch logic, and parameter structures for protected management functions are not disclosed in the available description; therefore, this report does not enumerate them.

Exploitation Scenarios

The following chain is derived strictly from the NVD description. Because no public proof-of-concept, exploit code, or Nuclei template is available, the sequence below describes the vulnerability class and mechanism at a technical level without fabricating implementation details.

1. Reconnaissance / target identification. An attacker scans for exposed Netcore NR256CN routers, typically using Shodan or similar internet-wide scanners. Devices present on public IP ranges with the NR256CN management web interface (identifiable via the l7_web_auth.cgi endpoint or vendor-specific banners) are enumerated. Default or non-default administrative credentials are irrelevant to the bypass, but confirming the management interface is reachable is the gate to exploitation.

2. Triggering the flaw. The attacker crafts an HTTP request whose URI begins with a route the server classifies as public — either l7_web_auth.cgi or an .ico asset route — while the request is actually structured to invoke a protected management CGI handler. Because the authorization layer treats any path carrying the public prefix as trusted, the request is passed through to the privileged handler without a session or credential check. This is the mechanism described in the CVE: prefixing the URI with a public route to reach protected handlers.

3. Payload / execution. The attacker directs the forged URI at management handlers that the device would normally require authentication to invoke. The exact request body and parameter encoding required by specific handlers are not specified in the available intelligence and are not invented here. At the vulnerability-class level, the effect is that the management endpoint executes the attacker's request as if it came from an authenticated session.

4. Post-exploitation impact. With access to protected management handlers, an attacker may read device configuration, alter network settings, adjust routing or firewall rules, and potentially modify administrative credentials. These actions correspond to the Low Confidentiality and Low Integrity impacts in the CVSS vector. The device may then be used as a pivot for network-adjacent activity, or its configuration tampered with to disrupt or redirect traffic. Note that exploitation requires the attacker to already know or discover the names of protected handlers (either through firmware analysis or request fuzzing).

Impact Assessment

CVE-2026-111712 targets the Netcore NR256CN router platform running firmware through 1.5.140116. Because the flaw is remotely reachable with no authentication and no user interaction, the blast radius includes all deployed NR256CN devices that are internet-facing or reachable from an attacker-controlled network segment. The CVSS 3.1 base score of 6.5 reflects a Medium severity with the following subscores:

• Attack Vector (N): Exploitable over the internet; no local access required.
• Attack Complexity (L): No special conditions — straightforward URI manipulation.
• Privileges Required (N): No credentials needed.
• User Interaction (N): No victim action required.
• Scope (U): Impact confined to the router itself.
• Confidentiality (L): Limited exposure of configuration or management data.
• Integrity (L): Limited ability to modify device settings.
• Availability (N): No direct denial-of-service component described.

Business impact hinges on device deployment context. In branch offices, retail sites, or SMB networks where Netcore routers serve as edge devices, an unauthenticated configuration compromise can undermine network segmentation, enable traffic manipulation, and expose internal management interfaces. Small-office routers are also commonly used as consumer-grade perimeter devices whose compromise can precede broader network intrusion.

Detection Guidance

Sigma Rule

title: Netcore NR256CN Authentication Bypass via URI Prefix Manipulation
id: 5f6d2a47-9c1e-4b8a-9e2f-netcore-288
status: experimental
description: Detects HTTP requests to Netcore NR256CN routers whose URI begins with l7_web_auth.cgi or an .ico asset route but is followed by additional path segments or CGI handler targets.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-111712
author: ValtersIT Threat Intelligence
date: 2026-01-01
tags:
  - attack.initial_access
  - attack.t1190
  - cve.2026.111712
logsource:
  category: webserver
  product: netcore
detection:
  selection_l7:
    cs-uri-stem|startswith:
      - '/l7_web_auth.cgi'
  selection_ico:
    cs-uri-stem|contains: '.ico'
  filter_legit_l7:
    cs-uri-stem|endswith:
      - '/l7_web_auth.cgi'
  filter_legit_ico:
    cs-uri-stem|endswith: '.ico'
  condition: (selection_l7 and not filter_legit_l7) or (selection_ico and not filter_legit_ico)
falsepositives:
  - Legitimate favicon or asset requests with query strings
level: medium

YARA Rule

rule CVE_2026_111712_Netcore_NR256CN_AuthBypass
{
    meta:
        description = "Detects firmware images or web resources of Netcore NR256CN exposing the l7_web_auth.cgi route associated with CVE-2026-111712"
        author = "ValtersIT Threat Intelligence"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-111712"
        cve = "CVE-2026-111712"
        date = "2026-01-01"
    strings:
        $a = "l7_web_auth.cgi" ascii wide nocase
        $b = "Netcore" ascii wide nocase
        $c = "NR256CN" ascii wide nocase
        $d = "1.5.140116" ascii wide
    condition:
        uint16(0) == 0x5A4D or (
            any of ($a) and ( any of ($b) or any of ($c) )
        ) or ( all of ($b, $c, $d) )
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-111712 Netcore NR256CN Auth Bypass via l7_web_auth.cgi Prefix"; flow:to_server,established; http.uri; content:"/l7_web_auth.cgi"; nocase; pcre:"/\/l7_web_auth\.cgi[^?]*\//i"; reference:cve,2026-111712; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-111712; classtype:web-application-attack; sid:2026111712; rev:1;)

alert http any any -> any any (msg:"CVE-2026-111712 Netcore NR256CN Auth Bypass via .ico Prefix to CGI Handler"; flow:to_server,established; http.uri; content:".ico"; nocase; content:".cgi"; nocase; distance:4; within:64; reference:cve,2026-111712; classtype:web-application-attack; sid:2026111713; rev:1;)

Elastic Detection

sequence by source.ip with maxspan=30s
  [network where network.protocol == "http" and url.path : ("/l7_web_auth.cgi/*" or "*.ico/*")]

Splunk SPL Query

index=web (cs_uri_stem="*/l7_web_auth.cgi/*" OR (cs_uri_stem="*.ico*" AND cs_uri_stem="*.cgi*"))
| where NOT (match(cs_uri_stem, "^.*/l7_web_auth\.cgi$") OR match(cs_uri_stem, ".*\.ico$"))
| stats count values(cs_uri_stem) as uris min(_time) as first_seen max(_time) as last_seen by src_ip dest_host
| convert ctime(first_seen) ctime(last_seen)
| sort - count

Wazuh OSSEC Rule

<group name="web_accesslog,netcore,cve-2026-111712,">
  <rule id="2026114" level="10">
    <decoded_as>web-accesslog</decoded_as>
    <url type="pcre2">/l7_web_auth\.cgi[^?]*/</url>
    <description>CVE-2026-111712: Netcore NR256CN auth bypass via l7_web_auth.cgi URI prefix</description>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
  <rule id="2026115" level="10">
    <decoded_as>web-accesslog</decoded_as>
    <url type="pcre2">\.ico[^?]*\.cgi</url>
    <description>CVE-2026-111712: Netcore NR256CN auth bypass via .ico URI prefix to CGI handler</description>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source). No vendor fix, workaround, or affected-version list has been published.

1. Immediate mitigations

• Remove Netcore NR256CN management interfaces from direct internet exposure. Restrict administrative access to a dedicated management VLAN or VPN, or firewall the web UI to trusted jump hosts.
• Front the device with a reverse proxy or WAF capable of enforcing strict URI allow/deny lists, blocking any request whose path contains additional segments after l7_web_auth.cgi or after an .ico asset reference.
• Monitor web access logs for requests to /l7_web_auth.cgi/* or .ico* paths that resolve to .cgi handlers, using the detection rules above.
• Rotate administrative credentials on any potentially exposed device and review configuration for unauthorized changes.

2. Patch/upgrade steps

• No patch is currently available. Contact Netcore support to confirm whether a fixed firmware release beyond 1.5.140116 has been issued, and track the vendor for an official advisory.
• When a fix is released, validate it in a lab, then upgrade affected NR256CN units during a maintenance window. Preserve configuration backups before firmware changes.

3. Long-term hardening

• Inventory all Netcore NR256CN deployments, including branch and remote sites; attest firmware versions.
• Enforce a policy that router management planes are never internet-facing; require out-of-band or VPN-only access.
• Segment IoT/SMB networking equipment from production segments and apply least-privilege firewall rules to limit lateral movement following compromise.
• Subscribe to vendor advisories and NVD updates; monitor for CISA KEV elevation of CVE-2026-111712, which would indicate active exploitation.

References

• NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-111712
• CWE-288: Authentication Bypass Using an Alternate Path or Channel — https://cwe.mitre.org/data/definitions/288.html
• MITRE ATT&CK T1190 — Exploit Public-Facing Application — https://attack.mitre.org/techniques/T1190/
• CISA Known Exploited Vulnerabilities Catalog (no listing as of this report) — https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• FIRST EPSS (not yet scored) — https://www.first.org/epss/

No public PoC, exploit code, Nuclei template, or evidence of in-the-wild exploitation currently exists for CVE-2026-111712. No threat actor campaigns have been publicly attributed.