CVE-2026-78050: Critical Stack Buffer Overflow in Comfast CF-N1-S Router

Overview

A critical stack-based buffer overflow vulnerability (CVSS 9.9) has been disclosed in the Comfast CF-N1-S wireless router, version 2.6.0.1. The flaw resides in the sub_41AD7C function within the web management interface, specifically at the /cgi-bin/mbox-config?method=SET&section=ntp_timezone endpoint.

Manipulation of either the timestr or ntp_client_enabled parameters with oversized or malformed input causes a stack-based buffer overflow, which can be leveraged to achieve remote code execution (RCE) on the affected device — a severe outcome for any router deployed at the network perimeter.

Technical Details

How the Vulnerability Works

The vulnerable endpoint accepts NTP configuration values via HTTP POST requests to the web management interface. The sub_41AD7C function processes the timestr and ntp_client_enabled fields without performing adequate bounds checking before copying user-supplied input into fixed-size stack buffers.

When an attacker sends an oversized value for either parameter, the overflow corrupts adjacent stack memory including the saved return address. This classic stack smashing technique can be used to redirect execution flow to attacker-controlled shellcode or return-oriented programming (ROP) chains, ultimately achieving full code execution under the process's privilege context — typically root on embedded devices.

Why the CVSS Score Is 9.9

The near-maximum CVSS score reflects:

• Network-accessible attack surface: The web management interface is reachable over LAN and potentially WAN if remote administration is enabled
• Low authentication requirement: The endpoint may be reachable with minimal or no authentication
• High impact across all three pillars: Confidentiality, Integrity, and Availability all rated HIGH
• No user interaction required: The attack is fully automated once a target is identified

Affected Systems

• Comfast CF-N1-S version 2.6.0.1 (confirmed)
• Other firmware versions have not been confirmed as patched or safe — treat all versions as potentially affected until a vendor advisory is issued

Comfast (全讯飞达) produces SOHO-grade wireless networking equipment widely deployed in small businesses and home office environments, particularly in Asia-Pacific markets. These devices often run with default credentials and have web management interfaces exposed on the local network.

Impact Assessment

If exploited, an attacker with network access to the router's management interface can:

1. Execute arbitrary code as root on the router
2. Pivot to other hosts on the network segments managed by the router
3. Intercept, modify, or redirect all traffic passing through the device
4. Establish persistence through firmware modification or configuration changes
5. Disable network services causing denial-of-service for connected devices

Recommended Mitigations

Until a vendor patch is available:

1. Restrict access to the web management interface — block port 80/443 on the router's WAN interface and restrict LAN access to trusted management hosts only
2. Disable remote administration if enabled
3. Apply network segmentation — place the router management interface on a dedicated management VLAN accessible only to administrators
4. Monitor for exploitation attempts — alert on unusual NTP configuration requests or unexpected outbound connections from the router
5. Consider replacement — if a vendor patch is not forthcoming, evaluate replacing affected devices with supported hardware

References

• NVD Entry: CVE-2026-78050
• CWE-121: Stack-Based Buffer Overflow