CVE-2026-76071 Overview
CVE-2026-76071 is a stack-based buffer overflow [CWE-121] affecting Netis NC63 firmware through version V3.0.0.3327. The flaw resides in the netis.cgi handler processing the ipFilterList=mod action. An unauthenticated remote attacker can supply an oversized destHost parameter to overwrite saved stack state. Because the Boa web server executes CGI processes as root, successful exploitation yields remote code execution with root privileges. The vulnerability is exploitable before authentication is verified, enabling network-based takeover of affected devices.
Critical Impact
Unauthenticated remote attackers can achieve root-level code execution on Netis NC63 devices by sending a crafted HTTP request to the ipFilterList=mod endpoint.
Affected Products
- Netis NC63 firmware versions through V3.0.0.3327
- Boa web server component running netis.cgi
- Devices exposing the management interface to untrusted networks
Discovery Timeline
- 2026-08-24 - CVE-2026-76071 published to NVD
- 2026-08-26 - Last updated in NVD database
Technical Details for CVE-2026-76071
Vulnerability Analysis
The vulnerability exists in the request handling path of netis.cgi when processing the ipFilterList=mod action. The CGI binary reads user-controlled input from the destHost parameter and copies it into a fixed-size buffer allocated on the stack. The copy uses sscanf conversions without a width specifier, so the length of user input is unbounded. Supplying a destHost value larger than the destination buffer overwrites adjacent stack frames, including the saved return address and register state. Because the check occurs before authentication is enforced, no credentials are required to reach the vulnerable code path.
Root Cause
The root cause is unsafe use of widthless sscanf format conversions when parsing query parameters. Format specifiers such as %s without a maximum field width copy input until a whitespace or null byte, ignoring the size of the destination buffer. Combined with the placement of authentication logic after parameter parsing, this creates a pre-auth memory corruption primitive.
Attack Vector
Exploitation requires only network reachability to the device's HTTP management interface. An attacker sends an HTTP request to netis.cgi with the ipFilterList=mod action and an oversized destHost value. The overflow overwrites the saved return address, redirecting execution to attacker-controlled data or gadgets within the CGI process. Since Boa spawns CGI handlers as root, the resulting shell or payload inherits full system privileges. Additional technical detail is available in the VulnCheck Security Advisory and the public proof-of-concept.
Detection Methods for CVE-2026-76071
Indicators of Compromise
- HTTP requests to netis.cgi containing the ipFilterList=mod action with abnormally long destHost values
- Unexpected child processes spawned by the Boa web server
- New listening sockets, reverse shells, or outbound connections originating from the device management plane
- Modifications to firmware configuration or persistence artifacts on the router file system
Detection Strategies
- Inspect web access logs for requests to /netis.cgi with ipFilterList=mod and measure the length of the destHost parameter
- Alert on non-printable or shellcode-like byte sequences in query strings targeting the router administrative interface
- Correlate crashes or reboots of the Boa web server with preceding HTTP requests to netis.cgi
Monitoring Recommendations
- Capture and retain HTTP request telemetry from network segments hosting Netis devices
- Baseline normal destHost parameter length and flag statistical outliers
- Monitor egress traffic from router management interfaces for connections to unfamiliar external hosts
How to Mitigate CVE-2026-76071
Immediate Actions Required
- Restrict access to the Netis NC63 management interface to trusted management VLANs or hosts only
- Disable remote WAN-side administration on affected devices
- Inventory Netis NC63 units and identify any running firmware at or below V3.0.0.3327
- Isolate or replace devices that cannot be updated or protected by network controls
Patch Information
At the time of publication, no vendor patch was referenced in the NVD entry for CVE-2026-76071. Consult the Netis NC63 product page and the VulnCheck Security Advisory for the latest firmware availability. Apply any released firmware update from Netis as soon as it becomes available.
Workarounds
- Place the router behind a network access control list that blocks inbound HTTP and HTTPS to the management port from untrusted networks
- Deploy a reverse proxy or web application firewall that enforces a strict maximum length on the destHost parameter and rejects requests to ipFilterList=mod from unauthorized sources
- Segment vulnerable devices so that compromise cannot pivot into sensitive internal networks
- Replace end-of-life or unsupported units with hardware that receives active security maintenance
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
