CVE-2026-108929

Executive Summary

CVE-2026-108929 is a critical argument injection vulnerability in the Netcore NR268 router firmware version 1.7.121109, specifically within the DDNS configuration component. An attacker with valid low-privileged credentials can remotely manipulate the Hostname argument processed by the execvp function in /router/DDNSset.cgi, leading to arbitrary argument injection. With a CVSS score of 9.9, successful exploitation allows full compromise of confidentiality, integrity, and availability across the scope-changed boundary of the device, making this a severe risk for affected deployments.

Technical Analysis

The vulnerability resides in the DDNS (Dynamic DNS) configuration handler of the Netcore NR268, a consumer/SOHO router. The NVD description indicates that the affected element is the execvp function called within /router/DDNSset.cgi. The execvp family of functions is used to execute external programs, taking an argument vector (argv). When user-controlled input — specifically the Hostname parameter — is passed into this argument vector without proper neutralization, an attacker can inject additional arguments or alter the command's behavior.

This is best classified under CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component, also known as Injection). The specific sub-class here is argument injection, where the attacker does not necessarily break out of the command itself but instead appends or modifies arguments passed to the underlying executable. This can be leveraged to alter the invoked program's functionality, force it to read or write unintended files, or trigger secondary behaviors such as loading alternate configuration files or executing auxiliary commands depending on the binary being called.

The attack surface is the router's web-based administrative interface, specifically the DDNS settings endpoint. Because the CVSS vector indicates PR:L (low privileges required), the attacker must possess some level of authenticated access — for example, a limited administrative user or a lower-privileged account — rather than being fully unauthenticated. The vector AV:N confirms the attack is network-accessible, and S:C (scope changed) indicates the impact extends beyond the vulnerable component itself, a common characteristic when a router is compromised and can then affect connected hosts or the broader network segment.

No patch, fixed version, or vendor advisory is currently identified. The description does not provide the exact binary invoked by execvp, so the precise downstream command and the full exploitation payload cannot be confirmed from available data.

Exploitation Scenarios

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

1. Reconnaissance / target identification. The attacker identifies Netcore NR268 devices exposed to the network, typically by scanning for the administrative web interface. Shodan searches using dorks such as product:"Netcore NR268" or http.html:"DDNSset.cgi" can locate candidate devices. The attacker confirms the firmware version is 1.7.121109 or otherwise affected.

2. Authentication. Because the CVSS vector requires low privileges (PR:L), the attacker must first obtain valid credentials. This may be achieved through default credential abuse, credential reuse, phishing, or prior compromise of a low-privileged account. The attacker then authenticates to the router's web interface.

3. Triggering the flaw. The attacker navigates to the DDNS configuration functionality and submits a crafted value for the Hostname argument. The input is passed into the argument vector of the execvp call in /router/DDNSset.cgi without adequate neutralization. The exact injected argument depends on the underlying binary invoked; the vulnerability description does not disclose that binary, so the precise payload cannot be specified here. At the vulnerability-class level, the injection manipulates arguments supplied to the executed program.

4. Post-exploitation impact. Given the CVSS base score of 9.9 with High confidentiality, integrity, and availability impacts and a scope change, successful argument injection can plausibly enable command execution or manipulation of the invoked utility, leading to full device compromise, configuration tampering, persistent access, and potential lateral movement into the network the router serves.

Impact Assessment

The CVSS 3.1 base score of 9.9 reflects a critical severity. The vector components are:

• AV:N — exploitable remotely over the network.
• AC:L — no special conditions beyond valid low-privileged access.
• PR:L — requires low privileges; the attacker needs authenticated access.
• UI:N — no user interaction required once access is obtained.
• S:C — scope is changed; impact extends beyond the vulnerable DDNS component.
• C:H / I:H / A:H — full loss of confidentiality, integrity, and availability.

Business impact includes total compromise of the router, which frequently functions as the network perimeter gateway. A compromised gateway can expose all downstream devices, allow traffic interception or redirection, enable persistent backdoor installation, and facilitate further attacks against internal systems. The scope change indicates that the security authority of the vulnerable component is exceeded, magnifying the blast radius. SOHO and branch-office deployments using the Netcore NR268 are at elevated risk, particularly where default or weak credentials remain in use.

Detection Guidance

Sigma Rule

title: Netcore NR268 DDNS Hostname Argument Injection Attempt
id: 6f2a9c1e-7b3d-4e8a-9c2f-1a5d6e7f8b90
status: experimental
description: Detects HTTP requests to the DDNS configuration CGI endpoint with suspicious characters in the Hostname parameter, indicative of argument injection against execvp in /router/DDNSset.cgi.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-108929
author: Threat Intelligence
date: 2026/01/01
logsource:
  category: webserver
  product: netcore
detection:
  selection_endpoint:
    cs-uri-stem|endswith: '/router/DDNSset.cgi'
  selection_method:
    cs-method: 'POST'
  selection_payload:
    cs-uri-query|contains:
      - 'Hostname='
      - '--'
      - ';'
      - '`'
      - '$(('
      - '|'
  condition: selection_endpoint and selection_method and selection_payload
falsepositives:
  - Legitimate hostnames containing hyphens or unusual characters (rare)
level: high
tags:
  - attack.t1190
  - cve.2026.108929

YARA Rule

rule CVE_2026_108929_Netcore_NR268_DDNS_ArgInjection
{
    meta:
        description = "Detects Netcore NR268 firmware references and DDNS CGI handler indicative of CVE-2026-108929 argument injection surface"
        author = "Threat Intelligence"
        date = "2026-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-108929"
        cve = "CVE-2026-108929"

    strings:
        $cgi   = "/router/DDNSset.cgi" ascii wide
        $func  = "execvp" ascii wide
        $host  = "Hostname" ascii wide
        $model = "NR268" ascii wide
        $ver   = "1.7.121109" ascii wide

    condition:
        uint32(0) == 0x464C457F and
        $cgi and $func and $host and
        ( $model or $ver )
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-108929 Netcore NR268 DDNS Hostname Argument Injection Attempt"; flow:established,to_server; http.method; content:"POST"; http.uri; content:"/router/DDNSset.cgi"; http_client_body; content:"Hostname"; nocase; pcre:"/Hostname=[^&]*(?:--|\||;|\x60|\$\(|&&)/i"; reference:cve,2026-108929; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-108929; classtype:web-application-attack; sid:2026108929; rev:1;)

Elastic Detection

network where
  network.protocol == "http" and
  http.request.method == "POST" and
  endsWith(url.path, "/router/DDNSset.cgi") and
  (contains(http.request.body, "--") or
   contains(http.request.body, ";") or
   contains(http.request.body, "$(") or
   contains(http.request.body, "`") or
   contains(http.request.body, "|")) and
  contains(http.request.body, "Hostname")

Splunk SPL Query

index=web OR index=proxy sourcetype=access_common OR sourcetype=stream:http
| search uri_path="/router/DDNSset.cgi" http_method="POST"
| eval payload=coalesce(form_data, http_request_body, uri_query)
| where match(payload, "(?i)Hostname=[^&]*(--|\\||;|\\x60|\\$\\(|&&)")
| stats count min(_time) as first_seen max(_time) as last_seen by src_ip, dest_ip, uri_path
| convert ctime(first_seen) ctime(last_seen)
| sort - count

Wazuh OSSEC Rule

<group name="netcore,cve-2026-108929,web,">
  <rule id="2026108" level="12">
    <if_sid>31100</if_sid>
    <id>^/router/DDNSset.cgi</id>
    <description>CVE-2026-108929 - Netcore NR268 DDNS Hostname argument injection attempt detected</description>
    <options>no_full_log</options>
  </rule>
  <rule id="2026109" level="12">
    <if_sid>31108</if_sid>
    <regex>Hostname=[^&amp;]*(--|\||;|\x60|\$\(|&amp;&amp;)</regex>
    <description>CVE-2026-108929 - Suspicious Hostname payload targeting DDNSset.cgi</description>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source).

1. Immediate mitigations.

   • Restrict network access to the router's administrative web interface to trusted management networks only; never expose the admin UI to the public internet.
   • Disable the DDNS feature if it is not operationally required, removing the vulnerable code path from exposure.
   • Enforce strong, unique administrative credentials and eliminate any low-privileged accounts unless strictly needed.
   • Apply network segmentation so that compromise of a single router does not grant broad lateral access.

2. Patch/upgrade steps.

   • No vendor patch or fixed firmware version is currently identified. Monitor Netcore's official support and advisory channels for an updated NR268 firmware release.
   • If feasible, replace affected devices with supported hardware offering current security maintenance.
   • Until a patch is available, treat affected devices as inherently untrusted endpoints and isolate accordingly.

3. Long-term hardening.

   • Adopt a firmware vulnerability management process that tracks vendor advisories and device end-of-support status.
   • Maintain an inventory of gateway/router assets with version tracking to rapidly identify exposure to future CVEs.
   • Implement web application firewall or reverse proxy filtering in front of any exposed management interfaces where feasible.
   • Apply least-privilege principles to all management accounts and enable auditing/logging of configuration changes.

References

• https://nvd.nist.gov/vuln/detail/CVE-2026-108929
• https://cwe.mitre.org/data/definitions/74.html
• https://attack.mitre.org/techniques/T1190/
• https://www.first.org/epss/ (EPSS not yet scored for this CVE)
• Netcore official support portal: https://www.netcore.in/ (monitor for NR268 firmware advisories)

No public PoC, exploit code, or evidence of active exploitation in the wild is currently available for CVE-2026-108929. No threat actor campaign has been attributed. CISA KEV status: not listed.