CVE-2026-94003: Comfast CF-N1-S Buffer Overflow Vulnerability

CVE-2026-94003 Overview

CVE-2026-94003 is a stack-based buffer overflow vulnerability in the Comfast CF-N1-S wireless device running firmware version 2.6.0.1. The flaw resides in the get_css_path_from_uri function within the /cgi-bin/mbox-config endpoint of the Web Management Interface. Attackers can exploit the vulnerability remotely over the network without authentication or user interaction. Public disclosure of the exploit details increases the likelihood of active weaponization against exposed devices. The vulnerability is tracked under CWE-119, covering improper restriction of operations within the bounds of a memory buffer.

Critical Impact
Unauthenticated remote attackers can trigger a stack-based buffer overflow in /cgi-bin/mbox-config, potentially leading to arbitrary code execution or full compromise of the affected device.

Affected Products

Comfast CF-N1-S firmware version 2.6.0.1
Web Management Interface component (/cgi-bin/mbox-config)
Devices exposing the management interface to untrusted networks

Discovery Timeline

2026-09-20 - CVE-2026-94003 published to the National Vulnerability Database
2026-09-24 - Last updated in NVD database

Technical Details for CVE-2026-94003

Vulnerability Analysis

The vulnerability exists in the get_css_path_from_uri function of the /cgi-bin/mbox-config CGI handler. This function processes URI input to derive a CSS resource path but fails to enforce proper bounds checking when copying attacker-controlled data into a fixed-size stack buffer. Sending a crafted request with an oversized URI parameter overwrites adjacent stack memory, including saved return addresses and function pointers.

Successful exploitation can corrupt program control flow, causing device crashes or enabling arbitrary code execution in the context of the web management process. Because CGI binaries on embedded devices typically run with elevated privileges, an attacker who achieves code execution can pivot to full device compromise. The attack requires no authentication and can be launched by any actor with network reachability to the management interface.

Root Cause

The root cause is improper restriction of operations within the bounds of a memory buffer [CWE-119]. The get_css_path_from_uri function performs unbounded string operations on user-supplied URI data without validating the input length against the destination stack buffer size. Embedded router firmware commonly relies on functions such as strcpy or sprintf, which do not enforce length limits and are prone to producing this class of defect.

Attack Vector

Exploitation occurs over the network by issuing a specially crafted HTTP request to the /cgi-bin/mbox-config endpoint on the device's Web Management Interface. The attacker controls the URI portion parsed by get_css_path_from_uri. No credentials, user interaction, or prior foothold are required. Devices with the management interface reachable from the internet or from untrusted network segments face immediate risk.

A public technical write-up describing the flaw is available in the GitHub CVE Issue Discussion and the VulDB Vulnerability Overview.

Detection Methods for CVE-2026-94003

Indicators of Compromise

HTTP requests targeting /cgi-bin/mbox-config containing abnormally long URI strings or CSS path parameters
Unexpected restarts, crashes, or watchdog-triggered reboots of the Comfast CF-N1-S device
Outbound connections from the device to unknown external hosts following management interface access
Web server or CGI process log entries showing malformed requests preceding service disruption

Detection Strategies

Deploy network intrusion detection signatures that identify oversized URI parameters directed at /cgi-bin/mbox-config
Monitor HTTP traffic to the device management interface for anomalous request lengths and unusual character sequences
Correlate device availability alerts with prior HTTP request patterns to identify potential exploitation attempts
Baseline expected administrative traffic and alert on requests originating from unauthorized source addresses

Monitoring Recommendations

Log and forward all inbound HTTP requests to Comfast device management interfaces to a centralized SIEM
Alert on any external internet-facing exposure of /cgi-bin/mbox-config discovered through asset discovery scans
Track firmware versions across the fleet to prioritize devices still running the vulnerable 2.6.0.1 release
Review network flow data for unexpected lateral movement originating from Comfast devices

How to Mitigate CVE-2026-94003

Immediate Actions Required

Remove the Comfast CF-N1-S Web Management Interface from all untrusted networks, especially the public internet
Restrict management access to a dedicated administrative VLAN or via VPN-only reachability
Audit all deployed Comfast CF-N1-S devices and identify those running firmware 2.6.0.1
Rotate any credentials that may have been exposed on affected devices and review configuration for signs of tampering

Patch Information

At the time of publication, no vendor patch has been referenced in the available advisories for CVE-2026-94003. Monitor the VulDB CVE Detail Page and the vendor's official channels for firmware updates. Until a fixed firmware release is available, network-level compensating controls should be treated as the primary defense.

Workarounds

Block inbound access to TCP port 80 and TCP port 443 on the device from all untrusted sources using upstream firewalls
Disable remote management functionality on the device if operationally feasible
Place vulnerable devices behind a reverse proxy or web application firewall configured to drop requests with excessively long URIs to /cgi-bin/mbox-config
Consider replacing end-of-life or unpatched devices with actively supported hardware

bash

# Example upstream firewall rule to restrict management access to a trusted subnet
iptables -A FORWARD -p tcp -d <comfast_device_ip> --dport 80 \
  -s 10.0.10.0/24 -j ACCEPT
iptables -A FORWARD -p tcp -d <comfast_device_ip> --dport 80 -j DROP