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CVE-2026-76071 – Pre-Auth Remote Code Execution – Netis NC63 Router (Firmware ≤ 3.0.0.3327)

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Summary

CVE-2026-76071 is a critical stack-based buffer overflow vulnerability in Netis NC63 router firmware through version V3.0.0.3327. The flaw resides in the netis.cgi handler and allows an unauthenticated, remote attacker to overwrite saved stack state and achieve code execution as root. Given the lack of authentication requirements and the network attack vector, this vulnerability carries critical severity.

Technical details

  • Root cause: the ipFilterList=mod action in netis.cgi parses the destHost parameter using sscanf() with widthless scanset conversions (e.g. %[^,]), copying attacker-controlled data into fixed-size (16-byte) stack buffers with no bounds checking.
  • Trigger condition: submitting an oversized, comma-free string in the destHost field is sufficient to overwrite the saved return address on the stack.
  • Attack vector: the vulnerable request is processed before any authentication check, so no valid session or credentials are required; the attacker only needs network access to the device’s management interface.
  • Impact: successful exploitation can yield arbitrary command execution with root privileges, enabling full device takeover, configuration theft, DNS manipulation, and interception of traffic passing through the router.

Affected software

  • Netis NC63 router firmware, all versions through V3.0.0.3327

Severity

  • CVSS v3.1 Base Score: 9.8 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  • (Also reported as CVSS v4.0: 9.3 Critical, CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N)

Mitigation and recommended actions

  • Immediate: no fixed firmware version has been published by Netis at this time; check the Netis support/download portal regularly for a firmware update addressing this issue and apply it as soon as it is released.
  • If no patch is available: restrict access to the router’s management interface (netis.cgi) to trusted internal networks only, disable remote/WAN administration, place management interfaces behind a VPN, and monitor for anomalous POST requests to the CGI endpoint handling ipFilterList actions.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • Server response header: netis
  • Page title: Shock&Innovation!! netis setup, netis ... Router, netis 광대역 라우터 관리 패널

References

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1

Map your entire attack surface (continously)

IONIX uses multi-factor discovery methods, including DNS analysis, certificate mapping, metadata inspection, and more, to automatically map every internet-facing asset across your environment. This includes cloud instances, third-party platforms, shadow IT, and even forgotten infrastructure that traditional tools miss.

2

Monitor for new CVEs

Dozens of threat intel feeds using agentic technology are continuously analyzed to detect the appearance of proof-of-concept code, exploit kits, and indicators of active targeting. IONIX goes further by applying AI to proactively evaluate whether emerging vulnerabilities are likely to be exploited, even before PoCs go public.

3

Identify Potential External Exposures

Not all CVEs matter. IONIX filters vulnerabilities by asking attacker-centric questions: Can it be reached from the internet? Does it require authentication? Is it being exploited in the wild? This dramatically reduces noise and focuses teams on threats that can actually be weaponized.

4

Create Safe, Scalable Exploit Validations

IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

5

Execute Exploit Validations

By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

6

Drive Fast and Actionable Remediation

Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

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