CVE-2026-76070: Netis NC63 Router RCE Vulnerability

CVE-2026-76070 Overview

CVE-2026-76070 is a stack-based buffer overflow [CWE-121] in Netis NC63 firmware through version V3.0.0.3327. The flaw resides in the login handler within /bin/netis.cgi, which is served by the Boa web server. Unauthenticated remote attackers can submit an oversized Base64-encoded password to overwrite saved stack state. The custom Base64 decoder does not validate output length against the fixed-size stack buffer, enabling memory corruption. Because the Boa web server executes CGI processes as root, successful exploitation yields remote code execution with root privileges on the device.

Critical Impact
Unauthenticated remote attackers can achieve root-level code execution on affected Netis NC63 routers by sending a single crafted login request.

Affected Products

Netis NC63 router firmware versions up to and including V3.0.0.3327
Boa web server component shipped with NC63 firmware
/bin/netis.cgi login handler binary on affected devices

Discovery Timeline

2026-08-24 - CVE-2026-76070 published to NVD
2026-08-24 - Last updated in NVD database

Technical Details for CVE-2026-76070

Vulnerability Analysis

The vulnerability lives in the login authentication path of the netis.cgi binary. When a client submits credentials, the handler extracts the Base64-encoded password field and passes it to a custom Base64 decoder. The decoder writes decoded bytes directly into a fixed-size buffer allocated on the stack, without comparing the projected output length against the destination size. An attacker who supplies a long enough Base64 string overflows the buffer and corrupts saved registers and the return address on the stack.

Because the Boa web server invokes CGI programs as root, code executed after a successful overflow inherits root privileges. This makes the device fully controllable through a single unauthenticated HTTP request.

Root Cause

The root cause is missing output-length validation in the custom Base64 decoder used by the login handler. Standard Base64 decoding produces approximately 3/4 bytes of output per input byte, but the decoder never bounds this against the fixed stack buffer capacity. This is a classic [CWE-121] stack-based buffer overflow triggered by attacker-controlled input length.

Attack Vector

Exploitation requires only network reachability to the router's HTTP management interface. The attacker sends a POST request to the login endpoint with a Base64-encoded password field long enough to overflow the target buffer and control the return address. No authentication, user interaction, or prior access is required. Additional technical analysis is available in the OzcanPNG blog on CVE-2026-76070, the GitHub PoC for CVE-2026-76070, and the VulnCheck advisory on NC63 overflow.

No verified sanitized exploitation code is republished here. Consult the referenced proof-of-concept repository for technical details.

Detection Methods for CVE-2026-76070

Indicators of Compromise

Unusually long password parameter values in POST requests to /bin/netis.cgi or the router login endpoint.
HTTP request bodies containing Base64 strings that decode to lengths far exceeding a normal password.
New or unexpected outbound connections initiated by the router shortly after inbound HTTP login traffic.
Unexpected processes spawned by the Boa web server or netis.cgi running as root.

Detection Strategies

Inspect HTTP traffic to the router management interface for password field lengths exceeding a reasonable threshold (for example, 128 bytes).
Alert on repeated failed login POSTs from a single source that carry oversized Base64 payloads.
Correlate router log entries showing netis.cgi crashes or restarts with preceding external HTTP requests.

Monitoring Recommendations

Restrict access to the router administration interface to trusted management networks and monitor that segment for anomalous HTTP activity.
Capture network flow data at the WAN and management VLAN boundary to identify scanning and exploitation attempts against affected devices.
Track firmware versions across the fleet and alert when devices running vulnerable NC63 builds appear on the network.

How to Mitigate CVE-2026-76070

Immediate Actions Required

Disable remote (WAN-side) administrative access to the NC63 web interface until a fixed firmware is available.
Restrict LAN-side access to the management interface using ACLs or a dedicated management VLAN.
Inventory all Netis NC63 devices and confirm firmware versions against the affected range up to V3.0.0.3327.

Patch Information

At the time of publication, no vendor advisory URL or fixed firmware version is listed in the NVD entry. Administrators should monitor the Netis NC63 product page and the VulnCheck advisory on NC63 overflow for updated firmware releases addressing the login handler.

Workarounds

Place vulnerable NC63 devices behind an upstream firewall that blocks unsolicited inbound HTTP and HTTPS to the router's management interface.
Enforce source-IP restrictions so that only jump hosts or administrator workstations can reach the login endpoint.
Where feasible, replace end-of-support NC63 hardware with a device family that receives active security maintenance.

bash

# Configuration example: block external access to the router management interface
# (apply on an upstream firewall; adjust interface and subnet values for your environment)
iptables -A FORWARD -p tcp -d <router_ip> --dport 80  -j DROP
iptables -A FORWARD -p tcp -d <router_ip> --dport 443 -j DROP
iptables -A FORWARD -p tcp -s <mgmt_subnet> -d <router_ip> --dport 80  -j ACCEPT
iptables -A FORWARD -p tcp -s <mgmt_subnet> -d <router_ip> --dport 443 -j ACCEPT